572 Chas. W. Hargitt 



recalled tbat Weismaxx describes the perisarc of P. cidaritis as only 

 a thiii, sliniy covering-, the height of the slender stemraed hydroid, 

 9 cm, is of itself most remarkable. So far as I am aware, no spe- 

 cies yet deseribed has a height of more thau ahout 8 mm, except 

 P. nmscoides, in which the height is doubtfully given as 2 to 3 

 inches. 



Concerning the characters and affinities of P. linearis there has 

 always been more or less doubt. It was originally deseribed by 

 Alder as Atracttjlis linearis, and was later referred b}- Allman^ 

 to the g:enus Perigonimiis, but with a confession of grave doubt as 

 to its real affinities, not haring himself seeu the species. I have 

 previously expressed some doubt as to the oceurrence of this species 

 at Naples. Speeimens from the collections preserved at the Zoo- 

 logica! Station and marked P. linearis {?), have proven to be quite 

 a different hydroid. And though I have sought during two Summers, 

 as intimated above, to secure the species it has not been found. 



Upon the two different occasions previously cited I have ob- 

 tained a hydroid which is undoubtedly a species of Pcrigonimus, 

 but have not been able to identify it with either of the species 

 above mentioned, nor with any other hitherto deseribed. It was 

 taken first in June, 1894, and again in April, May and June, 1903. 

 In both cases the hydroid colonies were vigorous and large, but no 

 gonads were present, a fact which would seem to suggest that the 

 breeding season had probably past, er perhaps had not yet arrived. 

 Weismann found his species in March, at which time gonophores 

 were present. My own observations cover a period from March 6 

 to July 30, so that it would seem stränge not to find some colonies 

 hearing gonophores, yet such have been the facts in the present case. 



In both instances the habitat of the colonies conforms well with 

 that of members of the genus generally, namely, a commensal one. 

 The hydroids were found in a few cases upon the shell of a shallow 

 water gasteropod, but in most abundance and in best condition upon 

 the margin of the carapace and upon the legs of a common crab, 

 Carciniis maenas. It is an interesting coincidence that the species 

 which it most resembles in general aspects, P. jonesii, of Long Is- 

 land, N. Y., has a similar habitat on the spider crab, Lihinia emar- 

 ginata. This commensal habit of Perigornmiis is a most interesting 

 one, though not peculiar, since it is shared by a considerable number 



1 Monogr. Gymnoblastic Hydroids. London 1871 pag. 329. 



