P0/1. Columbella rustica can be collected in thanatocenoses along beaches, by sight under water, and by touch in waist-deep water

The collections were conducted under three different conditions: in thanatocenoses along beaches, by sight under water and, by touch, in waist-deep water (table 1).

	Year	Recording	Collectors	Time		Nb. of C. rustica	Fragments
Thanatocenose
Argolide	2006-1	Described and measured	na			65	34
Argolide	2006-5	Described and measured	Na			20	0
Asini	2007-1	Described and measured	CP+PP			41
Asini	2007-3	Described and measured	CP + PP	35'		18
Asini	2008	Described and measured	CP + JB			58
Asini	2011-2	Described and measured	CP + PP+ SB	1h 10		248
Fourni	2006	Described and measured	MV+CP+BW			71
Franchthi	2007-1	Described and measured	CP			12
Kastraki	2011-1	Described and measured	CP + PP + SB	1h 30		216	59
Kastratki 2012		Described and measured	CP + SB	40’		51
Arvenitsa	2006	Described and measured	BW (+AC)			114
					total	914
Thanatocenose
Asini	2007-2	Counts by broad categories		1h 15'		123
Asini	2009-1	Counts by broad categories				22
Asini	2009-2	Counts by broad categories				81
					total	226
Under water, by sight
Asini and Arvenitsa	2009	Described and measured	CP + SM			74	0
Arvenitsa	2011-1	Described and measured	CP	45'		90	0
Andros	2011	Described and measured	CP			16	0
Arvenitsa	2012-4	Described and measured	CP	45’		92	0
					total	272
Under water, by touch
Arvenitsa nest	2012-1	Described and measured	CP	5'		22
Arvenitsa	2012-2	Described and measured	CP	45'		92
					total	114
Underwater, mixed (pred. by touch)
Arvenitsa	2012-3	Described and measured	CP	1h		203

P0/2. The dimensions of Columbella rustica vary depending on the places of collect

The modality and location of collect is an important factor which determines the mean size of the specimens collected and the ratio of specimens usable as beads. Size differences depending on the location of collection had previously been exemplified for live Patella vulgata (Bailey and Craighead 2003), but not, to our knowledge, for Columbella rustica.

The correlation between the height and maximum diameter of the shell is very high (Pearson’s R comprised between 0,83 and 0,93 depending on the assemblage, p< 0.01) and reaches similar values whether the samples are collected on beaches or underwater (table 2, figs 6 and 7). The height is thus sufficient to characterize the size distribution of the reference collections and compare them to the archaeological ones.

Location of collect	Year	Pearson’r	n	Type of collect
Arvenitsa	2006	0,88 (p < 0.01)	72	Thanatocenose
Arvenitsa	2012-4	0,83 (p < 0.01)	80	Underwater collect by sight
Arvenitsa and Asini	2009	0,89 (p < 0.01)	74	Underwater collectby sight
Arvenitsa	2012-1 and 2012-2	0,91 (p < 0.01)	112	Underwater collect by touch
Asini	2007-2008	0,83 (p < 0.01)	80	Thanatocenose
Argolide	2006-1	0,93 (p < 0.01)	67	Thanatocenose
Fourni	2006	0,89 (p < 0.01)	81	Thanatocenose

P0/3. The state of preservation varies widely according to the mode of collection (live or dead) and according to the beach

The state of preservation in reference collections is an important variable to assess the proportion of specimens in a good enough state to be perforated and the proportion of naturally holed shells that could be used directly as beads. To document the state of preservation, we have followed, with some modifications, Cartonnet’s classification (Cartonnet 1991).

• Class 1 corresponds to complete specimens, from the base to the apex. A slight deterioration of the apex is admitted, provided it does not create a hole.
• Class 2 corresponds to specimens that have lost one to three whorls on the spire, without reaching the last whorl.
• Class 3 corresponds to specimens that have lost all whorls but the last one, with a break at the level of the last suture.
• Class 4 corresponds to fragments unusable as ornaments.

Several other alterations can affect each class: large and small holes, broken lips or bases. We found few if any reference to the factors causing these deterioration. Cartonnet (1991) mentions the attack of predatory Muricidae on the last whorl as well as abrasion by the sand and shocks on rocks. Given the lack of precise criteria for diagnoses, we did not try to assign each perforation to a specific predator or to the mechanical actions of the waves and the sand. However, we distinguished the smaller holes (1 to 2 mm in diameter), probably mostly due to predators and smaller than the perforations found on archaeological specimens, and the larger holes, compatible with a direct use as beads and in large part certainly due to a violent shock on a rock. The position of the hole was noted for each specimen. We also recorded the cases when the lip was broken or missing. It seems that on the smallest specimens the lip was not formed and closed. These might be juveniles, but we did not find a confirmation. The various alterations that affect the shells lead to distinguish several subclasses within each class.

Thus, class 1a large includes complete specimens with a large enough hole to be used as bead (though the position of the hole is not always compatible with this use), class 1a small includes specimens with a holes smaller than archaeological ones, class 1bl specimens with a broken or missing lip, and class 1 bb the rare specimens with a broken base. The same subdivisions apply to the other classes. Fragments (class 4) are not included in the counts since they were not systematically collected.

As shown in Table 3, the state of preservation varies widely according to the mode of collect (live or dead) and according to the beach itself for thanatocenoses. Broken or perforated specimens are extremely rare in underwater samples, when they can be frequent in thanatocenoses. On the other hand, many specimens collected underwater are covered by micro-organisms and concretions (Fig. 4). Even when this is not the case, the presence of the periostrum, the organic outer layer of the shell, renders them much duller than beach-worn specimens. Dove shells found in thanathocenoses have been washed up on the beach after having been rolled by the waves. This abrasive process removes the concretions and micro-algae found on under-water specimens, and reveals their lustrous coloured outer surface. Within the thanatocenoses, the shells are better preserved on the sandy beach of Fourni than on Asini, where a range of low rocks separates the open water from the beach itself. The proportion of perforated specimens is also variable, but always low in our samples. It is lower than in the sample collected on the beach below Üçağızlı I Cave in Turquey (Stiner et al. 2013: 384), where they reach 20%, and than in the sample collected by Cartonnet in southern France (Cartonnet 1991), where it reached 45 %. When one only considers the specimens with a large dorsal perforation, as found on archaeological shell beads, it barely reaches 4 to 6% in our collections (10% at Üçağızlı I).

Class	1					2				3
Sub-class	1	1a	1a	1 bl	1bb	2	2a	2a	2 bl	3	3a	3a	3 bl	Total
		large	small				large	small			large	small
Thatanocenoses
Asini 2009	53,2	8,5		3,9	0,6	13,1	2,6			9,2	0,6			152
Asini 2011-a	40,9	1,2	0,8	4,5		38,1	2,4	1,6	0,8	8,1	0,8	0,4		244
Fourni 2006	61,4	5,7	4,2	15,7	2,8	5,7	1,4	1,4						70
Kastraki 2011 and 2012	52,4	4,8	2	6		20	2,8	2	1,6	3,6	3,2	0,4	0,4	250
Underwater collects
Arvenitsa 2011	96,7					2,1	1,1							91
Arvenitsa 2012-2	99,1					0,9								112
Arvenitsa 2012-4	91,3	1,1	1,1			5,4	1,1							92
Arvenista 2012-3	97,5	0,4		0,4		1,4								202

P0/4. The rates of collecting vary depending on the mode of collect and the beach

The rates of collecting in thanathocenoses were highly variable. On the same beach (Asini), it ranged from 11 to 80 shells per hour and per collector, fragments excluded (Table 4). This variation is independent of the aim of the collection: intact specimens only or all specimens. We did not systematically record individual variations between collectors, but is it clear that one of us (S. B.) was much more efficient than all others. Collecting by sight under water, and especially by poking for dove shell nests, is even more productive, reaching 200 specimens per hour and collector, all intact.

However, these relatively high figures do not mean it is easy to find Columbella rustica appropriate for bead making: many are either too small or broken when collected from thanatocenoses, or covered with concretions when collected in the sea. In all archaeological periods at Franchthi (Upper Palaeolithic, Lower Mesolithic, Upper Mesolithic, Final Mesolithic and Neolithic) 75% or more of the Columbella have a height ≥ 1,2 cm (Fig. 15). This figure can thus be considered the basic minimal standard for shells to be used as beads. It corresponds well to our empirical standards for perforating the shells by direct or indirect percussion without hitting our fingers rather than the shell. The mean height of the small Upper Palaeolithic sample of perforated dove shells actually reaches 1.42 cm (σ = 0,11, n = 10), while the larger Mesolithic sample has a mean of 1,34 cm (σ = 0.15, n = 58). Collecting from thanatocenoses on beaches by searching through the sand or gravels produced only 4 to 12 Columbella rustica of a height ≥ 1,2 cm per hour and per collector (Table 4).

Collect	Collectors	Time	Nb. of complete specimens	Nb. of specimens ≥ 1,2 cm	% of specimens ≥ 1,2 cm	Nb. of specimens ≥ 1,2 cm per hour and per collector
Thanatocenoses
Asini 2011-2	CP + PP + SB	1h10	248	27	15,7	7
Kastraki 2011-1	CP + PP + SB	1h 30	216	56	29,7	12
Kastraki 2012	CP + SB	40'	51	7	13,7	4
Asini 2007-2	CP + MV + PP	1h 15'	123	25	21,1	6
Underwater collects
Arvenitsa 2011-1	CP	45'	90	73	87,9	97
Arvenistsa 2012-4	CP	45'	92	72	91,1	96
Arvenitsa 2012-2	CP	45'	92	84	72,3	112
Arvenitsa	CP	1h	203	164	82,6	164

P1/1. Variation in the size distribution of Columbella rustica in archaeological samples may indicate changes in collection strategies

Seasonal variations in the size distribution of gastropods are often attributed to differences in environmental conditions or to the intensity of human exploitation (e.g. Álvarez-Fernández et al. 2011; Bailey and Craighead 2003; Guttiérez-Zugasti 2011). Our data show that, at least for Columbella rustica, the mode of collection is another potential factor of variation. Since the different modes of collection each induce specific constraints and advantages, various collection strategies may have been implemented according, in particular, to time constraints and aesthetic preferences.

P1/2. Collecting Columbella rustica on beaches (thanatocenoses) for beads, compatible to the dimensions of archaeological specimens, is time-consuming

The majority of archaeological specimens display the characteristic alterations of shells collected in thanatocenoses: pitting, rounding, breakage of the spire. However, while it is easy to collect dozens of Columbella rustica on a beach, finding specimens sufficiently well-preserved and large enough to be used as beads is time consuming on present-day Argolid beaches.

P1/3. On beaches, dove shells with a natural dorsal perforation are too rare to be the sole source of prehistoric beads.

Furthermore, we have seen that less than 10% of the shells collected on beaches were naturally perforated. Fewer still bore a dorsal perforation that allowed a direct use as bead. As an instance, on Asini beach (2009) we collected 6 Columbella rustica with a dorsal perforation comparable to the Palaeolithic and Mesolithic ones, over a total of 152. Consequently, we cannot concur with Cartonnet (1991: 304) in considering that the prehistoric bead-makers could rely only on naturally perforated specimens. In large assemblages such as found at Franchthi, the majority of the Columbella rustica beads were intentionally perforated.

P1/4. Collecting Columbella rustica underwater is efficient in terms of number and size of specimens, but provides duller shells

Given the much larger mean height of the shells collected underwater, the rate of collection of large specimens is much higher and can reach more than 150 usable shells per hour. However, at least a third is heavily covered with concretions. Even when the concretions are more superficial and the periostrum is scraped off, they remain much less shiny than shells collected in thanatocenoses.

P2/1. Collecting Columbella rustica for beads is the result of choices between quality and efficiency

In sum, collecting underwater, which, in optimal conditions, can be done without swimming, is by far the most efficient method, both by the number of specimens that can be collected per hour and by the proportion of specimens large enough to be transformed into beads. This holds true even when one discards the specimens covered with concretions, but the shells remain on the whole duller than Columbella rustica collected on beaches. When the snails are collected underwater, naturally perforated shells that could be used directly as beads are almost non-existant, and all perforations have to be manufactured. It is difficult to prove however, that this type of collect was practiced in archaeological times, since there are few diagnostic features besides the large mean height and the excellent state of preservation of the apex. At Franchthi, large specimens with intact apex are only abundant in the Neolithic.

It is easier to demonstrate that collecting on beaches, from thanatocenoses, has indeed been practiced: at Franchthi, most Palaeolithic and Mesolithic specimens display the characteristics of beach-worn shells — pitting, broken spire, abrasion. This mode of collection is much less productive, even on beaches that are not systematically combed for Columbella rustica such as Asini or Fourni, and may even be considered as time-consuming when one searches for specimens large enough to meet the size standards of the prehistoric shell beads. On the other hand, the shells are shiny and colourful, and a small proportion can be directly used as beads thanks to natural perforations. During these two periods at least, the preference has been given to the aesthetic quality of the shell rather than to the efficiency of the collection. Though not intrinsically rare, large and well-preserved specimens of dove shells can still be considered as valuable finds.