146 BULLETIN OF THE BUREAU OF FISHERIES. 



I. PELECYPODA. 



Of the bivalve mollusks 70 ( + 6?) species have been recorded belonging to 31 fami- 

 lies and 48 (+ 1 ?) genera. Of these, 57 species were taken during the Survey dredging 

 and 6 of them were new to the region when first collected by us. So far as known no 

 species new to science have been found. 



Verrill and Smith in 1873 listed 84 species of lamellibranchs, of which, however, 

 only 61 were recorded for specified points within the Woods Hole region, although the 

 stated ranges of 12 others would render their occurrence here probable. 



In subsequent papers Verrill added greatly to our knowledge of the north Atlantic 

 Mollusca, but most of these later papers dealt chiefly with collections made in much 

 deeper waters. 



Before Verrill, Gould (1 841, 1870) had catalogued the Mollusca of this state in his 

 well-known "Report on the Invertebrata of Massachusetts." There were here included 

 a large proportion of our Woods Hole species, though comparatively few definite records 

 are offered by Gould relating to the occurrence of mollusks within our region. 



It is worthy of note that, although our list of local Pelecypoda is probably fairly 

 complete, it is considerably exceeded by that comprised in each of the other faunal 

 catalogues which have been summarized in our comparative table. Thus the Canadian 

 list contains 100 species, the list for Plymouth 86, that for the Irish Sea io8( + 3?), and 

 that for the Gulf of Trieste 107. Thus, even in those cases where the areas comprised are 

 roughly comparable, the other regions exceed our own in the wealth of species. Of the 

 100 Canadian species 55 ( = 55 per cent of Canadian list, or about 75 per cent of our own) 

 are common to the Woods Hole region. On the other hand only 5 of the 86 Plymouth 

 species are known to be common to our own fauna. 



On an average 9.2 species of bivalve mollusks were taken per dredge haul at all of the 

 458 regular stations of the Survey. This figure is considerably larger than that repre- 

 senting any other class of organisms. The single species which was taken most fre- 

 quently was Area transversa, which was recorded from 264 of the stations. The following 

 is a complete list of those species which were taken at one-fourth or more of our dredging 

 stations, the species being arranged in order of frequency : 



Number of stations. 



Area transversa 264 



Anomia simplex 256 



Ensis directus 235 



Clidiophora gouldiana 234 



Spisula solidissima \ .• 222 



Cardium pinnulatum 219 



Mytilus edulis 217 



Nucula proxima 205 



Tellina tenera 193 



Callocardia morrhuana 192 



Crassinella mactracea 1S2 



Pecten gibbus borealis 162 



Corbula contracta 128 



Modiolus modiolus 120 



» As already pointed out, a careful study of synonymy might result in somewhat 



