Genus Myrtea Turton 1822 



Myrtea pristiphora Dall and Simpson 1902. Lamellated lucina. 

 Figure 68. 



This species is found at Puerto Rico (Abbott 1974). 



There are eight specimens from four samples of this species 

 in the NEFC collection (Table 5). 



The NEFC samples are from the continental shelf ranging 

 from the central part to the southern tip of Florida (Fig. 68; 

 Theroux and Wigley footnote 4, table 117). 



Abbott (1974) reported the depth range for this species to be 

 55 to 82 m. 



Our samples are from depths between 250 and 310 m with a 

 mean of 281 m. All of our samples and specimens are in the 

 200-499 m depth range grouping. 



Fifty percent of the samples occurred in each of two sedi- 

 ment types, silty sand and silt; silty sand substrates contained 

 75%, and silt, 25% of the specimens. 



Genus Parvilucina Dall 1901 



Parvilucina blanda (Dall and Simpson 1902). Three-ridged luci- 

 na. Figure 84. 



The distribution of this species is from North Carolina to 

 Brazil (Abbott 1974). 



Parvilucina blanda is a moderately common southern 

 bivalve of which there are six specimens from five samples in 

 the NEFC collection (Table 5). 



The samples in the NEFC collection are distributed on the 

 continental shelf from south of Cape Hatteras, N.C. , to slight- 

 ly north of Jacksonville, Fla. (Fig. 84; Theroux and Wigley 

 footnote 4, table 144). 



Abbott (1974) reported the depth range of this species to be 

 from 18 to 37 m. 



Our samples range in depth between 15 and 35 m with a 

 mean of 26 m. The majority of both samples and specimens, 

 80% for the former and 83% for the latter, are in the 25-49 m 

 depth range grouping with 20% of the samples and 17% of the 

 specimens in the 0-24 m grouping (Table 140). 



Sand was the predominant substrate type inhabited by 

 Parvilucina blanda in our collection with 60% of the samples 

 and 67% of the specimens occurring in this substrate type; 

 both sand-shell and silty sand each contained 20% of the 

 samples and 17% of the specimens (Table 141). 



Family THYASIRIDAE 

 Genus Axinopsida Sars 1878 



Axinopsida orbiculata (G. O. Sars 1878). Figure 17. 



The general distribution of this species is from Greenland to 

 Casco Bay, Maine (Johnson 1934; La Rocque 1953; Abbott 

 1974). Ockelmann (1958) listed a widespread occurrence in 

 Arctic regions and considered it to extend to north of Cape 

 Cod, Mass. The distribution of variety inaequalis according 

 to Johnson (1934) and Abbott (1974) is in the Bay of Fundy 

 and the Gulf of Maine. 



The NEFC collection contains one specimen of Axinopsida 

 orbiculata from one sample (Table 5). Although a final deter- 



mination has not yet been made, we suspect that, due to its 

 distribution, it is the variety inaequalis Verrill and Bush 1898 

 of this species. 



Our sample was obtained in Vineyard Sound, Mass. (Fig. 

 17; Theroux and Wigley footnote 4, table 26). 



The zoogeographic provinces occupied by this species are 

 the panarctic and Atlanto-arctic (Ockelmann 1958), while 

 Gosner (1971) placed it in the Boreal. 



In Atlantic waters, A. orbiculata is found at depths of from 

 18 to 55 m (Abbott 1974), while in the Arctic it ranges from 2 to 

 944 m (Ockelmann 1958). The variety inaequalis, according to 

 Johnson (1934) and Abbott (1974), is found in waters from 33 

 to 64 m deep. Our specimen was captured at a depth of 3 m. 



The only information pertaining to sediments we have 

 found relates to our sample which was in a sand substrate. 



Genus Thyasira Lamarck 1818 

 Thyasira brevis Verrill and Bush 1898. Figure 108. 



Johnson (1934), Clarke (1962), and Abbott (1974) reported 

 this species as being distributed from Georges Bank to off 

 Cape Hatteras, N.C. 



There are three specimens of this uncommon tiny bivalve in 

 the NEFC collection from one sample (Table 5). 



Our sample is from the upper continental slope south of 

 Nantucket Shoals. Mass. (Fig. 108; Theroux and Wigley foot- 

 note 4, table 195). 



The bathymetric range of this bivalve is from 183 to 3,340 m 

 (Abbott 1974). 



Our sample is from a depth of 440 m which places it in the 

 200-499 m depth range grouping. 



The sample was obtained from a sand bottom. 



Thyasira croulinensis Jeffreys 1847. Figure 108. 



This species is widely distributed throughout Arctic re- 

 gions, western Europe and into the Mediterranean Sea, it 

 occurs from West Greenland to off Bermuda in the northwest 

 Atlantic (Johnson 1934; La Rocque 1953, Ockelmann 1958; 

 Clarke 1962; Tebble 1966; Abbott 1974). 



This tiny bivalve is represented in the NEFC collection by 

 four specimens from three samples (Table 5). 



One of our samples is from the coast of Maine, another from 

 the eastern portion of the Gulf of Maine, and the third sample 

 is on the Southern New England shelf west of Nantucket 

 Shoals (Fig. 108; Theroux and Wigley footnote 4, table 196). 



Ockelmann (1958) reported that the species is low Arctic- 

 boreal in distribution, it also occupies the Mediterranean- 

 Atlantic province, and is abyssal. 



Thyasira croulinensis enjoys a wide bathymetric range, 

 occupying water depths which range from 7 to 2.700 m 

 (Clarke 1962: Tebble 1966). 



Our samples are from water depths which range between 49 

 and 353 m with a mean of 153 m. In terms of depth range 

 groupings, 33% of the samples are in each of the 25-49, 50-99. 

 and the 200-499 m groupings, while the distribution of speci- 

 mens was 25% in the 25-49 and 50-99 m groupings, and 50% of 

 the specimens are in the 200-499 m grouping (Table 142). 



Three sediment types each contained 33% of the samples; 

 these were till, silty sand, and silt substrates. In terms of 

 specimens, till and silt contained 25%, while silty sand sub- 

 strates contained 50% of the specimens (Table 143). 



26 



