Our samples are distributed on the continental shelf from 

 just southeast of Cape Hatteras, N.C., south to the southern 

 third of Florida, north of Miami (Fig. 26; Theroux and Wigley 

 footnote 4, table 40). 



The 36 samples, yielding specimens of this taxon, are from 

 water depths ranging between 10 and 43 m with a mean of 21 

 m. Seventy-eight percent of the samples and 83% of the 

 specimens are in the 0-24 m depth range grouping, whereas 

 22% and 17% of the samples and specimens, respectively, are 

 in the 25-49 m grouping (Table 252). 



The majority of both samples and specimens occurred in 

 sand which contained 42 and 43%, respectively; the next 

 major substrate type was sand-shell, which contained 39 and 

 38% of samples and specimens, respectively. Shell substrates 

 accounted for 14% of the samples and 16% of the specimens, 

 while silty sand substrates accounted for 6 and 4%, respec- 

 tively (Table 253). 



Genus Gemma Deshayes 1853 

 Gemma gemma (Toten 1834). Amethyst gem clam. Figure 45. 



This tiny bivalve is very common to excessively abundant 

 (Abbott 1974; Emerson et al. 1976). 



Gemma gemma occurs from northern seas around New- 

 foundland to Florida and the Bahamas, and ranges into Texas 

 and along the Gulf Coast; it has also been introduced into the 

 Pacific at Puget Sound, Wash., and extends south to San 

 Francisco; in the Arctic it extends from the Parry Islands 

 south to and including Labrador (Johnson 1934; Morris 1951, 

 1973; La Rocque 1953; Ockelmann 1958; Abbott 1968, 1974; 

 Emerson et al. 1976). 



The NEFC collection contains 2,21 1 specimens represent- 

 ing 2% of the entire number of specimens from only 33 sam- 

 ples (Table 5). 



The distribution of the NEFC collection samples is patchy 

 although they did yield large numbers of specimens. The first 

 patch occurs in the Cape Cod region, the next small number of 

 samples is in Delaware Bay; another region from which sam- 

 ples were obtained is in Albemarle Sound and off the coast of 

 Cape Hatteras, N.C.. and another sampling site is on the 

 continental shelf to the east of Jacksonville, Fla. (Fig. 45; 

 Theroux and Wigley footnote 4, table 74). 



This species is found in the Boreal. Virginian, and Caroli- 

 nian zoogeographic provinces (Coomans 1962); Gosner 

 (1971) placed it in the Boreal and Virginian provinces. 



The depth range of the amethyst gem clam is from the 

 littoral zone to 30 m (Morris 1951; Abbott 1968, 1974; Gosner 

 1971; Porter 1974). 



The depth range of our samples is to 66 m with a mean of 6 

 m. Ninety-four percent of the samples and nearly 100% of the 

 specimens are in the 0-24 m depth range grouping; 3% of the 

 samples are in the 25-49 m and 50-99 m groupings with each 

 accounting for < 0.1% of the specimens (Table 254). 



This species occurs on sandy shores (Morris 1951). 



Our samples were found in three sediment types: sand- 

 shell, sand, and silty sand. Sand substrates accounted for 75% 

 of the samples but only 15% of the specimens, while sand- 

 shell substrates contained 6% of the samples but 80% of the 

 specimens; silty sand contained 19% of the samples and 5% of 

 the specimens (Table 255). Seventeen samples containing 

 1,803 specimens are unclassified with regard to sediment 

 type. 



Genus Liocyma Dall 1870 



Liocyma fluctuosa (Gould 1841). Fluctuating liocyma. Figure 

 54. 



This northern species is found in both the Atlantic and 

 Pacific Oceans. In the Atlantic it occurs from Greenland to 

 Nova Scotia and in the Pacific from Alaska to British Colum- 

 bia (Johnson 1934; La Rocque 1953; Clarke 1962; Morris 

 1973; Abbott 1974). Ockelmann (1958), who reported its 

 occurrence in Arctic regions, stated that it is panarctic and 

 probably truly circumpolar. 



This moderately common bivalve species is represented in 

 the NEFC collection by 22 specimens from 1 sample (Table 

 5). 



Our sample is from the Scotian Shelf (Fig. 54; Theroux and 

 Wigley footnote 4, table 91). 



Ockelmann (1958) reported it as occurring in from 2 to 228 

 m of water; Clarke (1962) reported it as occurring in from 18 to 

 2,440 m of water, but stated that the authenticity of the 

 abyssal records is questionable. 



Our sample is from a depth of 51 m which places it in the 

 50-99 m depth range grouping. 



The sample was obtained from a gravel substratum. 



Genus Mercenaria Schumacher 1817 



Mercenaria mercenaria (Linne 1758). Northern quahog. Figure 

 61. 



Mercenaria mercenaria is the commercially important 

 bivalve also known as the hard shelled clam, quahog, stuffer, 

 cherry stone, or littleneck among other common names, 

 which vary from locality to locality within its range. Landings 

 in 1978 produced 13.3 million pounds of meat, valued at $29.7 

 million (Pileggi and Thompson 1979). 



The normal distribution of this species is from the Gulf of 

 St. Lawrence to Florida, into the Gulf of Mexico, south to the 

 Yucatan Peninsula; further, Mercenaria mercenaria has been 

 introduced to Humboldt Bay, Calif., and into England and 

 other European waters (Johnson 1934; Morris 1951, 1973; La 

 Rocque 1953; Ockelmann 1958; Tebble 1966; Abbott 1968, 

 1974; Emerson et al. 1976). 



Although it is very common and locally very abundant 

 within our study area, there are only 21 specimens from 9 

 samples in the NEFC collection (Table 5). This paucity of 

 material is directly attributable to this species preference for 

 intertidal and shallow water habitats which are not normally 

 sampled during research cruises conducted by this Center. 



The majority of our samples are from the Cape Cod region 

 with one sample from the coast of New York (Fig. 61; Ther- 

 oux and Wigley footnote 4, table 106). 



The zoogeographic distribution of this species is Boreal, 

 Virginian, and Carolinian in the western Atlantic, and Celtic 

 in Europe (Coomans 1962). Gosner (1971) considered it 

 Boreal and Virginian, while Dance (1974) placed it in the 

 Boreal province in eastern North America as well as in the 

 Transatlantic, Caribbean, and Californian provinces. 



As previously mentioned this is a shallow water organism 

 ranging from between tide marks down to only a few meters 

 depth (Gosner 1971; Morris 1973). 



46 



