on the Southern Coast of Neio England. 93 



habited almost exclusively by northern forms, or an extension 

 of the Acadian fauna. 



There is also a corresponding difference in the temperature 

 of the water, the change in some cases amounting 5° F., both 

 at the surface and bottom, within a distance of two miles, and 

 without much change in the depth ; and consequently there 

 must be an offshoot of the arctic current setting into the 

 middle of the sound, although the shores feel the influence of 

 the Gulf-stream, as shown by the occurrence of southern 

 forms of pelagic animals in their waters. 



The shores of Buzzard's Bay and Vineyard Sound present 

 nearly all varieties of stations, and are therefore favourable 

 for collecting ; they are occupied, except on some of the 

 outer islands, by an assemblage of animals characteristic of 

 the coasts further south, and known as the Virginian fauna. 

 A few northern forms occur, however, on the rocky shores, 

 which do not extend as far as New Haven. Among these 

 Purpura lapillus is most conspicuous. This shell is asso- 

 ciated there with Eurosalpinx cinerea^ in about equal numbers ; 

 but at New Haven the latter occurs alone, while on the 

 northern coasts of New England the Purpura is found unac- 

 companied by the other, which is rarely found north of Cape 

 Cod. But in nearly all other respects the littoral fauna is 

 very similar to that of the vicinity of New Haven, or the 

 coasts further south, as far as Cape Hatteras, making allow- 

 ance only for differences in the stations, and especially for the 

 absence of rocks south of New York. 



In Vineyard Sound and Buzzard's Bay the water is every- 

 where shallow, usually from 3 to 8 fathoms deep, and rarely 

 exceeding 12 or 14 fathoms, even in mid-channel. In Vine- 

 yard Sound the bottom is generally sandy, and extensive reefs 

 of shifting sands are numerous and often nearly destitute of 

 life ; but extensive regions of gravelly and shelly bottoms 

 occur, and these are often almost completely covered by 

 several species of compound ascidians growing in large 

 masses. One of these, which forms large hemispherical or 

 irregular masses, made up of an aggregation of long slender 

 colonies, united together at their bases and usually thickly 

 covered throughout with sand, is very abundant, often en- 

 tirely filling the dredge with masses up to six inches in 

 diameter : this is the Amoiiroucium pellucidum^ Verrill. 

 Another one, nearly as abundant, forms smooth cartilaginous 

 masses in the form of flat lobes, crests, and plates, sometimes 

 two feet long and about an inch thick, the surface covered 

 with stellate colonies, while the colour of the masses is of a 

 delicate bluish or sea-green tint by reflected light, although 



