98 CHAS. W. HARGITT. 



tide-pools, sometimes to the extent of several square feet. The 

 same fact has also been pointed out by McCrady, Leidy, and 

 others. During the current season I have records of the follow- 

 ing modes of life : The general occurrence on shells occupied by 

 hermit crabs ; the maxillipeds of the lobster ; the chela of the 

 common crab, Cancer irroratus ; stems of common rock-weed ; 

 dredged in Vineyard Sound on bit of waterlogged oak timber ; 

 finally in immense masses from piles of docks at Vineyard Haven, 

 and still later from the carapace and legs of Limulus. The 

 occurrence on the appendages of the crab and lobster are suffi- 

 ciently similar to that on the shell of the hermit crab to make it 

 devoid of special significance. But the occurrence and distribu- 

 tion in the other cases are certainly not compatible with any 

 necessary commensal relations. On the other hand they go to 

 confirm the suggestion made above, and also long ago suggested 

 by Agassiz, that there is probably no essential advantage to this 

 hydroid in its habitat on the shell of the crab. Certainly in the 

 enormous colonies of the hydroid on these stationary substrata 

 we cannot perceive any adverse conditions so far as the animals 

 are concerned, for not only were the vegetative conditions among 

 the most remarkable known, as shown by the enormous colonies, 

 but they were apparently in the height of sexual development, 

 both male and female colonies being abundant, and ladened with 

 gonads. 



The second feature to be noted, as intimated above, is the 

 question as to the specific distinctness of local species. As is 

 well known, Agassiz regarded it as specifically distinct from the 

 European H. echinata, and designated the species as H. polyclina. 

 In my Synopsis (op. cit.), I followed Allman in his rather em- 

 phatic doubt on this point, and designated the species as H. 

 echinata. In connection with the unusual numbers taken during 

 the present season, and their range of habit, I took occasion to 

 go carefully over the subject once more, reviewing as carefully 

 as possible all the evidence available, and find myself unable to 

 distinguish any good grounds for regarding these two species, 

 so-called, as sufficiently different to warrant the distinction. And 

 when one recalls the fact that two systematists of the acknowl- 

 edged renown of McCrady and Leidy both regard our species as 



