BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. II3 



ture, is probably responsible for the greater prevalence of this species in the western 

 half of Vineyard Sound, where, as we have pointed out elsewhere, certain typical sand- 

 dwelling species find their most congenial habitat. 



On the other hand, certain less frequent species (not among those charted) were 

 dredged chiefly upon muddy bottoms. Particularly worthy of mention is the holo- 

 thurian Caudina arenata, which was taken by us seven time's in Buzzards Bay and only 

 once in Vineyard Sound. 



The part played by temperature in determining distribution is rather strikingly 

 illustrated by some members of our echinoderm fauna. The local distribution of the 

 two commoner species of Asterias is quite in keeping with what we know of the ranges 

 of these two forms upon our coast. A glance at charts 48 and 49 shows us that whereas 

 Asterias forbesi has a practically unrestricted distribution in local waters, A. vulgaris, 

 on the contrary, is most prevalent in the colder portion of Vineyard Sound. Indeed, 

 there is seen to be a progressive concentration of the distribution symbols as we pass 

 from the eastern to the western end of the Sound, while in the Bay the records are con- 

 fined to the neighborhood of the open ocean. It is likewise worth noting in this con- 

 nection that the latter species was recorded from all seven of our regular dredging 

 stations at Crab Ledge, while Aslerias forbesi was recorded but once. 



As stated by Clark, the range of the latter species upon our coast is from "Maine to 

 the Gulf of Mexico," but it is said to be "rare or local north of Cape Ann." It is pri- 

 marily a shallow water form, which does not appear to pass beyond depths of 25 or 30 

 fathoms. A. vulgaris, on the other hand, ranges from Labrador to Cape Hatteras, 

 though it is "rarely seen in shallow water * * * south of the Woods Hole regjion." 

 It is recorded from depths as great as 358 fathoms. 



Such natural expectations as to distribution in local waters are not, however, 

 realized in the case of another starfish, Henricia sanguinolenla. This species, also, is 

 listed as "littoral only as far south as the Woods Hole region," while, to the northward, 

 it extends to Greenland. The dredging records show it to be abundant throughout 

 the length of Vineyard Sound and, indeed, to be rather commoner in the eastern 

 (warmer) half. It is likewise recorded from scattered stations in Buzzards Bay, even 

 well toward its head. For this species, then, temperature seems to be a minor factor in 

 determining the distribution in local waters. 



Of considerable interest are the relative distributions of our two local sea urchins, 

 Arbacia puiwiulata and Strongylocentrotus droebachie^isis . The former species appears 

 to be of general occurrence throughout Vineyard Sound, except for the portion adjoining 

 the open ocean. In Buzzards Bay it occurs as far as the upper end, but it seems here 

 to be restricted largely to the vicinity of land. Strongylocentrotus , on the other hand, 

 occurs in greatest abundance in the western portion of Vineyard Sound, though occa- 

 sional specimens have been taken as far eastward as West Chop. In Buzzards Bay it 

 is found only near the extreme lower end. Again, Strongylocentrotus was taken at all 

 seven of the stations at Crab Ledge, while Arbacia was not found there once. The 

 latter species occurs locally at all depths, even up to the low-water mark. The former 

 species, on the other hand, is rarely if ever taken at such slight depths, except in 

 northern waters." We have very few records of its occurrence in less than 5 fathoms, 



a Verrill. it is true, states that this species occurs "at low water on the outer rocky shores. " This can not be a common occur- 

 rence locally, however. 



16269°— Bull. 31, Pt I— 13 8 



