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(+17?) 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 (1841, 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 108(+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 moiiusks 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 Arca 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. 
AT CANtLAanS VEPs iiss 5: elas haiy See ie Meee aoe ite aah cise s)id v0 Ses Sepa ealeMe exes Siecle Rene cece ane 264 
PDO AIST PLE 6 oF oc cc me peer EN Te sos o's «14 elous patel erage GND orate mares 256 
TISSUE EIES ser oe oc eo tre MER so os. 9 sd oo 2 tea era eae ee Bea rae 235 
Clidiophoracol dianaty.<.er esr eee et asc as = oss oe Satara Meet larmanete Siem eiats 234 
Spisularsalidisciasale tit eee eee ete Fes RS ad Re ae Nea ona a 222 
asd etter paris pla tenia yc ee ae ee A tee eo ot Sop eter ae ae ee I a oy 219 
Moy tilts ett iy jstsr yey ioh eee an NE chan fda asi Men earth ia SUH pe 217 
Ny fiver NEI 0) (o>. 6 hoe maa etsie- so dtl) Cd Coe eRe inns Acstio Sb eo MeRS aa ea 205 
Mellin CEMeLA sas es hee eee oe 8 cin skin ern AR eee aly Ce aaa he 193 
Callocardia morrhttanalts saree seta ek oe ae ee ele wena, 192 
Crassiniella:mactracea’s 2s ati eee Meee etl e sae ce aes ts se eee eRe as che eee ae 182 
Pecten'gibbts borealis. 709-/Syee atest ctr cieleic) cisco: Les. oe eee eter entiss = ieee eee 162 
Cotbula contractas, 3, 25 tevwisr a eres NaS ool aes! $y, scope Sidiol pet AE tour inst Cai anregae 128 
GCOS THIOCIONIS. 5 is cke cies te cura ee eS 2 a fools 2)" ata ogee at sae eg 120 
@ As already pointed out, a careful study of synonymy might result in somewhat increasing this number. 
2 
