BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 99 



(Verrill) to the Gulf of St. Lawrence (Whiteaves). It is thus predominantly a northern 

 form, which here approaches the southern limit of its range. Temperature is, with 

 little doubt, the determining factor in the distribution of this species in local waters. 



What appears to be a type of distribution exactly converse to the last is to be 

 found in the case of the simple coral, Astrangia darus. This species is abundant and 

 of very general distribution throughout most of Buzzards Bay and Vineyard Sound. 

 Indeed, it seems to be almost equally at home upon every sort of bottom, including 

 soft black mud. Now, it will be seen that this form is conspicuously scarce at the open 

 end of Vineyard Sound, i. e., in those same colder waters to which Alcyonium seems 

 adapted to live. Astrangia, we learn, is a southern species, finding its northward limit 

 at or near Cape Cod, so that its scarcity in the colder waters of the region is thus perhaps 

 explained. It may be suggested, on the other hand, that this gap in the local distribu- 

 tion of Astrangia may result from the character of the bottom, which is almost wholly 

 sandy throughout the area in question. The species has, however, been dredged else- 

 where upon bottoms of practically pure sand, so that this explanation does not seem 

 sufficient. 



If we seek for comparisons between the distributions of different members of the 

 same genus, we find that our dredging records furnish few data of importance upon this 

 subject. Tubularia couthouyi and T. crocea are seen to present certain characteristic 

 differences, in that the former is largely restricted to stony bottoms, while the latter is 

 of much more general occurrence upon the local sea floor and is abundant, likewise, 

 even upon piles, etc., in shallow water. The former species has not been taken with 

 living hydranths during the summer months, except at Crab Ledge and in the deeper 

 waters south of Marthas Vineyard, while T. crocea has been found within the region in 

 an active condition throughout the summer. 



Referring to the two commoner species of Eudendrium (E. ramosum and E. dispar), 

 it would seem probable that the distribution of the latter in local waters is far more 

 restricted than that of the former. Indeed, our records point to the scarcity or 

 absence of this species in Buzzards Bay, 6 a condition which affords an interesting con- 

 trast to that of E. ramosum, one of the few hydroids which were dredged with any 

 frequency in the latter body of water. 



Even more striking differences of habitat shown by closely related species of 

 ccelenterates might be chosen among genera which do not figure in our dredging records 

 at all, e. g., Edwardsia and Sagartia. 



The following is a list of the species taken in the course of the Survey dredging. As 

 usual, those species are designated by an asterisk which were taken at 10 or more of the 

 stations : 



HYDROZOA. 



Ectopleura prolifica. 

 *Pennaria tiarella (chart 14). 



Podocoryne carnea. 

 *Hydractinia echinata (chart 15). 

 *Eudendrium ramosum (chart 16). 

 * Eudendrium dispar (chart 17). 



Eudendrium carneum. 



Eudendrium capillare. 



Eudendrium album. 

 *Tubularia couthouyi (chart ic 

 PTubularia spectabilis. 



Tubularia tenella. 



a It was not found by us at Crab Ledge. 



t> In the course of the 29 supplementary dredge hauls in Buzzards Bay in 1909, E. ramosum was taken eight times, but E. 

 dispar was not noted once. 



