Character and Distribution of the genus Peiigonimus. 481 



nevertheless of a nature analogous to tlic more liig'hly specialized 

 skeletons of the higher forms, as well as homologous in many points. 



I have not been able to obtain more thau a single species from 

 the Naples bay, though two bave been reported, viz. P. linearis, 

 Alder, by Du Plessis^ in 1880, and the species described as new 

 by Weismann in 1883, namely, P. cidaritis. 



The species P. litiearis has also obtained record in the Station 

 faunal list, but I am rather disposed to doubt its occurrence bere, 

 as protracted search with the dredge under the most varied circum- 

 stances faiied to procure it. It sliould be said, however, that P. cida- 

 ritis was found in limited numbers and in poor condition. In bis 

 studies of the Hydroids of the bay in 1883, Weismann did not find 

 the species, but found the one he described, in the same habitat as 

 had been given for litiearis. It would seem probable thereforc that 

 only one cxists in these waters. 



This, moreover, seems to be in general accord with the distri- 

 bution of the genus, in only a few cases a given locality affording 

 a habitat for more than one species. 



A careful comparative study of P. cidaritis with P. Jonesii has 

 led to the following results: 



1. A more intimate morphological relationship than seems to 

 exist between auy other members of the genus, at least in so far as 

 pertains to the hydrozooid persons. I have not been able to obtain 

 gonozooids of the former species, and have only the descriptions of 

 Weismann as a basis of comparison. Both species have similarly a 

 simple perisarc, though in P. cidaritis it is somewhat more dense, 

 and slightly chitinized in the older portions of the stem. The bathy- 

 metrical ränge of the species is very nearly the same, varying from 

 10 to 30 fathoms. 



They differ in their host habitat, P. cidaritis being chiefly, p os- 

 si bly whoUy, found upon the sea-urchin Dorocidaris papillata\ P. 

 Jonesii being found thus far only upon the spider crab, Lihinia 

 emarginata. 



2. An exceedingly simple, or gen'eralized character. This is 

 n both the hydrozooid and gonozooid persons, specially the 



former. The morphological characters are very similar to those of 

 the lower Tubularians, and the skeletal features would seem to rank 

 with those of the simj)lest of the Gymnoblastic Hydroids. 



1 Mitth. Z. Stat. Neapel 2. Band 1S80 pag. 143. 



32* 



