Specimens ofCuspidaria occurred in all but two of our nine 

 sediment types, namely, shell and sand-shell. The greatest 

 numbers of samples and specimens occurred in clay which 

 yielded 41% of the former and 45% of the latter; another 

 sediment type which contained substantial amounts was silty 

 sand accounting for 30% of the samples and 30% of the 

 specimens; sand yielded 11% of the samples and 11% of the 

 specimens with smaller amounts of samples and specimens 

 occurring in the remaining sediment types (Table 323). There 

 are three samples containing eight specimens which are un- 

 classified with regard to sediment type. 



Genus Plectodon Carpenter 1864 



Plectodon sp. Figure 90. 



The NEFC collection contains six specimens from four 

 samples which bear the generic designation Plectodon sp. 

 (Table 5). 



The samples containing this taxon are from the edge of the 

 continental shelf in the Mid-Atlantic Bight region between 

 Chesapeake Bay and Delaware Bay (Fig. 90; Theroux and 

 Wigley footnote 4. table 156). 



The range in depth for these four samples is 77 to 1 1 8 m with 

 a mean of 100 m. Seventy-five percent of the samples and 83% 

 of the specimens are in the 100-199 m depth range grouping 

 with 25% of the former and 17% of the latter in the 50-99 m 

 grouping (Table 324). 



Two sediment types contained Plectodon specimens, these 

 were sand-shell and sand; the former contained 75% of the 

 samples and 83% of the specimens and the latter 25% of the 

 samples and 17% of the specimens (Table 325). 



Family VERTICORDIIDAE 

 Genus Lyonsiella Sars 1868 



Lyonsiella abyssicola (G. Sars 1872). Figure 57. 



This species is reportedly found south of Martha's 

 Vineyard, Mass., (Johnson 1934; Abbott 1974) but also 

 occurs in northern Europe and in Arctic regions (Ockelmann 

 1958; Clarke 1962). 



The NEFC collection contains one specimen from one 

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



Our sample is from slightly south of the northeast peak of 

 Georges Bank at the juncture of the continental shelf and the 

 upper portion of the continental slope (Fig. 57; Theroux and 

 Wigley footnote 4, table 99). 



Ockelmann (1958) reported that this species is panarctic- 

 boreal and that it is abyssal in the North Atlantic only. 



This species enjoys a wide bathymetric range occupying 

 water depths between 37 and 2,654 m (Clarke 1962). 



Our sample is from a water depth of 617 m which places it in 

 the 500-999 m depth range grouping. 



Our sample was obtained from a sand substrate. 



Lyonsiella sp. Figure 57. 



Abbott (1974) noted that members of this genus are mostly 

 very deep water inhabitants and that there are several Atlan- 

 tic species. The NEFC collection contains one specimen from 

 one sample (Table 5). 



Our sample is from the continental slope adjacent to the 

 entrance to Northeast Channel (Fig. 57; Theroux and Wigley 

 footnote 4, table 100). It is from a water depth of 1 ,934 m in a 

 silty sand substrate. 



Genus Verticordia Gray 1840 



Verticordia ornata (Orbigny 1842). Ornate verticord. Figure 

 117. 



This species occurs in both the Atlantic and Pacific Oceans; 

 in the Atlantic it ranges from Massachusetts to Florida, and 

 the West Indies, it also occurs at Bermuda and Brazil; in the 

 Pacific Ocean it occurs from Catalina Island, Calif., south to 

 Panama (Johnson 1934; Morris 1973; Abbott 1974). 



This species is represented in our collection by eight speci- 

 mens from seven samples (Table 5). 



The NEFC samples are from the east coast continental 

 shelf between Cape Fear, N.C., and the central section of the 

 Florida Peninsula (Fig. 117; Theroux and Wigley footnote 4, 

 table 208). 



This species occupies the Virginian, Caribbean, and Caroli- 

 nian zoogeographic provinces (Coomans 1962). 



The ornate verticord enjoys a rather wide bathymetric 

 range, occurring in water depths which range between 9 and 

 1,257 m (Johnson 1934; Abbott 1974). 



Our samples are from water depths which range between 30 

 and 420 m with a mean of 148 m. The majority of both samples 

 and specimens in our collection are in the 25-49 m depth range 

 grouping which contains 57% of the samples and 63% of the 

 specimens; the 200-499 m grouping contains 29% of the sam- 

 ples and 25% of the specimens, while the 100-199 m grouping 

 contains 14% of the samples and 13% of the specimens (Table 

 326). 



All of our samples yielding specimens of the ornate verti- 

 cord were obtained in sand substrates (Table 327). 



ACKNOWLEDGMENTS 



We wish to thank the many persons who assisted in the 

 preparation of this report. In particular Harriett E. Murray 

 who provided invaluable assistance in sorting, coding, and 

 catalogue preparation and maintenance as well as manuscript 

 preparation. 



Assistance in specimen identification was provided by 

 Arthur S. Merrill, Yashuhiko Kamada, and Christopher P. 

 Ciano at the NEFC, while Cyclocardia novangliae deter- 

 minations were made at the University of Rhode Island by 

 John J. Kosmark. 



Ellen Winchell, Rodman E. Taylor Jr., Amy Leventer, and 

 Jacki Murray assisted in record maintenance, data reduction, 

 tabulating, auditing, and plotting distributions. 



The bivalve sketches were done from life by Betsy Pratt, 

 and Teresa C. Ellis, while John R. Lamont provided drafting 

 expertise. 



John P. Laird and Philip H. Chase Jr. assisted in the genera- 

 tion of many computer programs required for the automatic 

 processing of this voluminous data base. 



We also wish to thank Ruth D. Turner, Mollusk Depart- 

 ment, Museum of Comparative Zoology, Harvard Universi- 

 ty, for critical review of the manuscript and many helpful 

 suggestions regarding organization of the manuscript to make 

 it more useful to the reader. 



58 



