Thyasira elliptica Verrill and Bush 1898. Figure 108. 



Johnson (1934), Clarke (1962), and Abbott (1974) all stated 

 that this species is found off Martha's Vineyard, Mass. 



The NEFC collection contains 12 specimens from 4 sam- 

 ples of this rather rare bivalve species (Table 5). 



Our samples are from the New England region, one sample 

 off the coast of Maine, two south of Martha's Vineyard, 

 Mass.. at the edge of the continental shelf, and another in the 

 Middle Atlantic Bight off Long Island, N.Y. (Fig. 108; Ther- 

 oux and Wigley footnote 4. table 197). 



The above cited authors all state one depth occurrence for 

 this species at 2,655 m. 



Our samples containing Thyasira elliptica are from water 

 depths which range between 64 and 1 14 m with a mean of 91 

 m. Seventy-five percent of the samples and 92% of the speci- 

 mens are in the 50-99 m depth range grouping, and 25% of the 

 samples and 8% of the specimens are in the 100-199 m group- 

 ing (Table 144). 



Clay substrates contained 75% of the samples and 67% of 

 the specimens, while sand sediments contained 25% of the 

 samples and 33% of the specimens (Table 145). 



Thyasira equalis Verrill and Bush 1898. Figure 109. 



This species occurs in various sections of the Arctic, the 

 north Eurasian continent and Norway, and in the northwest 

 Atlantic it ranges from Nova Scotia to Chesapeake Bay (John- 

 son 1934; La Rocque 1953; Ockelmann 1958; Clarke 1962; 

 Abbott 1974). 



Thyasira equalis is represented in the NEFC collection by 

 309 specimens from 44 samples (Table 5). 



The NEFC suite of samples ranges from the environs of 

 Nova Scotia down through the Gulf of Maine and Georges 

 Bank region to the Middle Atlantic Bight region off Atlantic 

 City, N.J. (Fig. 109; Theroux and Wigley footnote 4, table 

 198). 



Ockelmann (1958) considered the distribution of this spe- 

 cies as being probably panarctic and abyssal in the North 

 Atlantic only. 



The above cited authors report the depth range for this 

 species as occurring between 172 to 2,813 m. 



Our samples are from depths which range between 37 and 

 2,910 m with a mean of 283 m which could possibly be an 

 extension of existing depth records. In terms of depth range 

 groupings the mid-depth groupings contain almost equal 

 amounts of samples and specimens. In order of increasing 

 depth range the abundance of samples and specimens is as 

 follows: the 25-49 m depth range grouping contains 5% of the 

 samples and 3% of the specimens; the 50-99 m grouping, 14% 

 of the samples and 19% of the specimens; the 100-199 m 

 grouping contains 34% of the former and 28% of the latter, 

 while the 200-499 m grouping contains the same amount of 

 samples (34%) and 25% of the specimens; the 500-999 m 

 grouping contains 11% of the samples and 25% of the speci- 

 mens, while the 2,000-3,999 m grouping contains 2% of the 

 samples and 0.3% of the specimens (Table 146). 



Members of this species were obtained from four sediment 

 types. Sand substrates contained 1 1% of the samples and 12% 

 of the specimens; silty sand contained 32% of the samples and 

 36% of the specimens; silt sediments contained 7% of the 



former and 4% of the latter, while clay contained the largest 

 amounts, 50% of the samples and 48% of the specimens 

 (Table 147). 



Thyasira ferruginea Winckworth 1932. Figure 110. 



This species enjoys a wide distribution in both Atlantic and 

 Pacific Oceans and also extends possibly worldwide. In the 

 Atlantic it ranges from Arctic seas to off North Carolina, 

 while in the North Pacific it ranges from the Aleutian Islands 

 to Alaska; it also occurs at Scotland and the North Sea, in the 

 Mediterranean, and at the Madeira Islands; it has also been 

 reported from off the coast of Africa, off the coast of India, 

 and possibly into Antarctic regions; it has also been recorded 

 from the Mid-Atlantic Ridge region (Johnson 1934; La 

 Rocque 1953; Clarke 1962; Tebble 1966; Abbott 1974). 



Our collection contains 1,381 specimens from 92 samples of 

 this small bivalve species which, among the members of the 

 genus Thyasira, is the most abundant in our waters (Table 5). 



Our samples are distributed from the northeast peak of 

 Georges Bank on the upper reaches of the continental slope, 

 south to Cape Hatteras, N.C., with one sample occurring in 

 the complex of Massachusetts and Cape Cod bays (Fig. 110; 

 Theroux and Wigley footnote 4, table 199). 



As well as enjoying wide geographic distribution, this spe- 

 cies is also widely distributed with depth ranging from 20 to 

 3,000 m (Clarke 1962; Tebble 1966). 



The NEFC samples are from water depths which range 

 between 41 and 2,715 m with a mean of 1,388 m. The 25-49 m 

 and the 50-99 m depth range groupings each contain 1% of the 

 samples and < 0.5% of the specimens; the 200-499 m grouping 

 contains 8% of the samples and 6% of the specimens, while 

 the 500-999 m grouping contains 28% of the samples and the 

 largest amount of specimens, 54%; the 1,000-1,999 m group- 

 ing contains the largest amount of samples, 37%, and 20% of 

 the specimens, while the 2,000-3,999 m grouping contains 

 25% of the samples and 20% of the specimens (Table 148). 



Thyasira ferruginea appears to prefer silty substrates to 

 others for its habitat. Silty sand substrates contained 26% of 

 the samples and 45% of the specimens, while silt sediments 

 contained 50% of the samples and 43% of the specimens; clay 

 sediments contained 15% of the samples and 5% of the speci- 

 mens with sand containing the smallest amounts of both, 9% 

 of samples and 6% of specimens (Table 149). 



Thyasira flexuosa Verrill and Bush 1898. Figure 111. 



This species is reported to occur in both the North Atlantic 

 and North Pacific Oceans. In the Atlantic it ranges from 

 Greenland to off North Carolina but has also been reported 

 from Norway, Western Europe, and the Mediterranean; 

 whereas in the Pacific it ranges from the Bering Sea to off San 

 Diego, Calif. (Johnson 1934; La Rocque 1953; Ockelmann 

 1958; Clarke 1962; Abbott 1974). 



This tiny bivalve is represented in the NEFC collection by 

 1,044 specimens from 104 samples each of which make up 1% 

 of their respective groups (Table 5). 



Our samples are from the Gulf of Maine-Nova Scotian shelf 

 region, around the periphery of Georges Bank, south onto the 

 Southern New England continental shelf and slope region. 

 with two samples, in deep water, off the mouth of Chesapeake 

 Bay (Fig. Ill; Theroux and Wigley footnote 4, table 200). 



27 



