148 BULLETIN OF THE BUREAU OF FISHERIES. 



Restricted wholly or chiefly to the Sound. 

 Anomia aculeata. 

 Pecten magellanicus. 



Modiolus modiolus (a few inshore stations in Bay). 

 Crenella glandula. 

 Area ponderosa. 

 Venericardia borealis. 

 Thracia conradi. 



Restricted wholly or chiefly to the Bay. 

 Area pexata. 

 Yoldia limatula. 



Solemya velum (confined to inshore stations). 

 Lsevicardium mortoni (most abundant at inshore stations). 

 Venus mercenaria. 



Tagelus gibbus (confined to inshore stations). 

 Macoma tenta. 

 Mulinia lateralis. 

 Mya arenaria (confined to inshore stations). 



It will be noted that even some of those species which are restricted to Buzzards Bay 

 {Solemya velum, Tagelus gibbus, Mya arenaria) are found there only at the inshore 

 stations. Another species which is, on the whole, restricted to these stations, both in 

 the Bay and the Sound, is Lyonsia hyalina. 



An analysis of our records shows that certain species appear to exhibit marked 

 preferences as to the depth of the water which they occupy. The following, for example, 

 are in considerable degree restricted to depths of 5 fathoms or less: 



Pecten gibbus. Tagelus gibbus. 



Area pexata. Lyonsia hyalina. 



Solemya velum. Mya arenaria. 



Four of these six species are those which have just been mentioned as restricted to 

 the inshore stations. 



Species which were dredged most frequently at depths of 10 fathoms or more" are: 



Pecten magellanicus. Astarte undata. 



Modiolus modiolus. Astarte castanea. 



Modiolaria nigra. Cyclas islandica. 



Crenella glandula. Thracia conradi. 

 Venericardia borealis. 



With the exception of the two species of Astarte, all of those comprised in this last 

 list will be found in the list of predominantly northern species given below. And, with 

 the exception of Astarte castanea and Modiolus modiolus, all are more or less restricted 

 to the colder portions of the Sound and the Bay.*" Reference to the charts shows that 

 the remaining seven species occur wholly or predominantly in the western half of Vineyard 

 Sound and the lower end of Buzzards Bay. Five of these species {Pecten magellanicus, 

 Crenella glandula, Venericardia borealis, Astarte undata, and Cyclas islandica) were like- 

 wise taken at Crab Ledge, where, as we have seen, many of our typical colder water 



« Depths of 10 fathoms or more were recorded at only 36 per cent of the 45S stations. All these species were, nevertheless, 

 dredged an absolutely greater numhcr of times at such depths. 



ii As stated above (p. 28), the western half of Vineyard Sound is little ii any deeper than the eastern half. Tlic greater average 

 depth at which these species occurred results from the fact that they were rarely taken near shore. Thus they figure but little in 

 the Phalaropc dredgings. 



