1230 BULLETIN OF THE BUREAU OF FISHERIES. 



doubtless interferes with the respiratory currents of many others. Since Vine- 

 yard Sound and Buzzards Bay are rather sharply distinguished from one 

 another by the presence or absence of mud on the one hand and of clean sand 

 and gravel on the other (pi. cxxiv), it is natural that the most obvious distinc- 

 tion in distribution should be that between the predominantly sound-dwelling 

 species and the predominantly bay-dwelling ones. The former, it must be 

 added, greatly preponderate over the latter numerically. Within each 

 of these large bodies of water the local distribution of many forms is very 

 obviously determined by the occurrence of one or another variety of bottom. 

 Thus it happens that many species whose occurrence in Vineyard Sound is 

 general are found in Buzzards Bay only in the adlittoral zone, particularly 

 along the Elizabeth Islands (fig. 6). Here the mud is less prevalent, and bot- 

 toms of clear sand and gravel are frequently met with. 



A type of distribution which is almost the converse of the last is encountered 

 in the case of certain mud-dwelling species which are of general occurrence 

 throughout the bottom of Buzzards Bay, but which in Vineyard Sound are 

 confined to a few definite areas where mud is known to be present (e. g., the 

 annelid ClymcneUa torquata and the bivalve moUusk Yoldia limatula, figure 7 

 and 8). Furthermore, Vineyard Sound is roughly divisible into an eastern half, 

 in which the bottom is predominantly stony and gravelly, and a western half, in 

 which the bottom is mainly of sand. Accordingly, many species, particularly 

 attached forms (fig. 9), are scarce or absent in the western half of the Sound, 

 except in the littoral and sublittoral zones, while certain sand-dwelling forms, 

 among which we may name the rays and the flounders among the fishes (fig. 

 ID, 11), and the lady-crab {Ovalipes ocellatus), are especially common in that 

 very region. The lower end of Buzzards Bay is comparatively free from deposits 

 of mud, and accordingly we often meet with species here which are generally 

 distributed in the sound, but which are scarce or absent from the more central 

 parts of the bay. The scarcity or apparent total absence in Buzzards Bay of 

 many local species of animals representing every phylum, is, we believe, due 

 chiefly, if not entirely, to the character of the bottom. 



The temperature factor, with little doubt, is a controlling one in determin- 

 ing the distribution of many species within the limits of our chosen region. We 

 encounter a large number of animals, belonging to practically all the subking- 

 doms, and likewise certain plants, whose distribution in local waters is confined 

 to the western end of Vineyard Sound and the mouth of Buzzards Bay (fig. 13,14, 

 15, 17,27). Here the water temperature at the bottom averages during the sum- 

 mer months about 10° F. (5.6°C.) lower than at Woods Hole and in the le'ss exposed 

 waters of the region. (Fig. 2.) The mean bottom temperature at 14 stations 

 in the western third of Vineyard Sound and just without the latter, at a time when 

 it was probably near its maximum, was found by us to be 60.2° F. (15.7° C). 



