Our samples are from water depths which range between 46 

 and 271 m with a mean of 98 m. The majority of both samples 

 and specimens are in the 50-99 m depth range grouping which 

 contains 65% of the samples and 73% of the specimens, while 

 26% of the samples and 23% of the specimens are in the 

 100-199 m grouping; both the 25-49 and 200-499 m groupings 

 contain 4% of the samples and 1.3 and 1.9% of the specimens, 

 respectively (Table 40). 



Morris (1973) reported that Yoldia thraciaeformis is nor- 

 mally found in mud substrates. 



The majority of our samples and specimens occurred in 

 clay substrates which contained 49% of the samples and 42% 

 of the specimens while silt and silty sand substrates each 

 contained 12% of the samples, but 34 and 8%, respectively, of 

 the specimens. Other sediment types in which Yoldia thra- 

 ciaeformis were found were till with 24% of the samples and 

 15% of the specimens and gravel which contained 2% of the 

 samples and specimens (Table 41). There are 5 samples con- 

 taining 14 specimens which are unclassified with regard to 

 sediment type. 



Yoldia sp. Figure 121. 



The NEFC Specimen Reference Collection contains 303 

 specimens of bivalves from 88 samples which, since many 

 specimens had badly broken and/or eroded shells precluding 

 exact classification, were identified only to the generic level 

 Yoldia sp. (Table 5). 



Samples containing members of the genus Yoldia are from 

 the Gulf of Maine region extending from the Nova Scotian 

 shelf to Cape Cod; there is also a group occurring on the outer 

 continental shelf and upper slope from south of Cape Cod, 

 Mass. , into Long Island Sound (Fig. 121 ; Theroux and Wigley 

 footnote 4, table 215). 



The range of depth for these samples is 20 to 1 ,480 m with a 

 mean of 196 m. The majority of both samples and specimens 

 are in mid to lower continental shelf depth range groupings 

 with the bulk in the 100- 199 m grouping which contains 43% of 

 the samples and 51% of the specimens; the 200-499 m group- 

 ing contains 35% of the samples and 25% of the specimens, 

 while the 50-99 m grouping contains 15% of the samples and 

 20% of the specimens; 5% of the samples and 2% of the 

 specimens are in the 25-49 m grouping and each of the 0-24 m 

 and 1,000-1,999 m groupings contain 1% of the samples and 

 0.7 and 1.3%, respectively, of the specimens (Table 42). 



As with other members of this group the fine sediment 

 types were preferred over the coarser ones with the majority 

 of both samples (34%) and specimens (40%) occurring in clay 

 substrates; silty sand substrates accounted for 31% of both 

 samples and specimens, while silt contained 12% of the sam- 

 ples and 11% of the specimens; both till and sand substrates 

 each contained 10% of the samples, but 6 and 7%, respective- 

 ly, for the specimens, and the coarsest fractions, sand-gravel 

 and gravel, contained 2.4 and 1.2%, respectively for samples 

 and 5 and 0.4% , respectively, for specimens (Table 43). There 

 are 5 samples containing 3 1 specimens which are unclassified 

 with regard to sediment type. 



Genus Portlandia Moerch 1857. 



Portlandia fraterna (Verrill and Bush 1898). Figure 92. 



This species is widely distributed throughout Arctic regions 

 and also ranges from the Gulf of St. Lawrence to off Georgia; 



it is also found in northern Eurasia and in Norway (Johnson 

 1934; LaRocque 1953; Ockelmann 1958; Clarke 1962; Abbott 

 1974). 



There are three samples containing five specimens of this 

 tiny bivalve in the NEFC collection (Table 5). 



The NEFC samples are from the Gulf of Maine (Fig. 92; 

 Theroux and Wigley footnote 4, table 160). 



Ockelmann (1958) reported that this species is probably 

 panarctic and that it is abyssal in the North Atlantic only; 

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



The reported depth range for Portlandia fraterna is from 

 5.5 to 2,943 m (Johnson 1934; Clarke 1962; Abbott 1974). 



The range in depth of our samples is 183 to 211 m with a 

 mean of 196 m. The 100-199 m depth range grouping contains 

 67% of the samples and 60% of the specimens, while the only 

 other depth range, the 200-499 m grouping, contains 33% of 

 the samples and 40% of the specimens (Table 44). 



Samples containing Portlandia fraterna were found in silty 

 sand and clay sediments; the former contained 67% of the 

 samples and 60% of the specimens, the latter 33% of the 

 samples and 40% of the specimens (Table 45). 



Portlandia frigida (ToreU 1859). Figure 92. 



The presence of this small bivalve is questionable in our 

 waters according to Ockelmann (1958). He questioned the 

 occurrence of this species in New England waters as reported 

 by Verrill (1882a), and Verrill and Bush (1898), stating that it 

 is truly high Arctic in distribution. Pending a revision of the 

 group, and since our specimens agree with other investiga- 

 tor's descriptions and figures, we will tentatively maintain it 

 as presently identified. 



According to reports we have seen, this species is thought 

 to range from Arctic seas and the Gulf of St. Lawrence to 

 Massachusetts (Johnson 1934; LaRocque 1953; Clarke 1962: 

 Abbott 1974). However, Ockelmann, as stated above, consi- 

 dered it to occur only in Arctic regions and listed a fairly 

 widespread distribution for it there. 



There are five specimens from three samples of this species 

 in the NEFC collection (Table 5). Our samples are from the 

 Gulf of Maine north and east of Cape Cod (Fig. 92; Theroux 

 and Wigley footnote 4, table 161). 



The depth range for this species is between 6 and 2,297 m 

 (Clarke 1962; Abbott 1974). 



The NEFC samples are from depths which range between 

 55 and 213 m with a mean of 160 m. The samples are grouped 

 in two depth range groupings, the 50-99 m, which contains 

 33% of the samples and 20% of the specimens, and the 200-499 

 m grouping which contains 67% of the former and 80% of the 

 latter (Table 46). 



Thirty-three percent of our samples and 60% of our speci- 

 mens occurred in silty sand sediments, while 67% of the 

 samples and 40% of the specimens occurred in clay substrates 

 (Table 47). 



Portlandia inconspicua (Verrill and Bush 1898). Inconspicuous 

 yoldia. Figure 92. 



This species is distributed in the Arctic and occurs from 

 Nova Scotia to North Carolina in the northwestern Atlantic 

 (Johnson 1934; La Rocque 1953; Ockelmann 1958; Abbott 

 1974). 



