Notes ou some Hydromedusae from the Bay ut" X;iples. 571 



C. pendula. In so doing-, however, it shoukl be notecl that the at- 

 tachment of the polyps in the two cases is a ery different. In the 

 case of C. pendula there is a deep insinuation of the fÌDger-like 

 roots within the pensare of the base of the hvdroid, and usuallv 

 low amoug the rhizoidal iilaments of (he adults, while in the case 

 of T. mesemhryanthemum the attachment of the vouug- is purely 

 superficial, and occurs at anv place upon the stem. 



JPerigoniinus napolitanus sp. nov. (J) 



Of the twelve kuown species of Perigonimus but two have been 

 recorded from the Bay of Naples, namely, P. linearis Alder, by Du 

 Flessisi in ISSO, and P. cidaritis Weismaxn^, in 1883. Weismann 

 has contended that Du Plessis was mistaken in ascribiug bis spe- 

 cies to P. linearis^ believing- it to be that which he has described 

 as new under the last of the above named species. 



During- two different times, in 1894 and ag-ain in 1903, I have 

 sought to ideutify one or both these species among the Naples hy- 

 droid fauna but have not suceeeded. A hydroid taken from the 

 same habitat, uamely, the spines of the sea urchin, Dorocidaris 

 papillafa, in 1894 and at first thoug-ht to be the species recorded 

 by Du Plessis, was found to lack characters distinctive of the 

 species as described by Alder and moreover lacked also characters 

 enumerated by Weismann, particularly as to size, number of ten- 

 taeles, etc. both of the hydroid and medusa. Weismann's species 

 has been described as 9 cm high and to have 20 tentacles. The 

 medusa differs from those of most si)ecies in having 4 marginai 

 tentacles, and well developed orai tentacles with tufts of nettling- 

 Organs. 



Hartlaub '^ has called attention to the unusual characters of 

 Weismann's medusa and has suggested that they might reasonably 

 be assigned to a different genus, or even to a different family, so 

 far as their fundamental characteristics are concerned. 



When, in addition to this, one refleets that hydroids of com- 

 mensal habits, such as is the case with most or ali the species of 

 Perigonimus, are usuali}^ of small size, and when furthermore it is 



1 Mitth. Z. Stat. Neapel 2. Bd. 1S80 pag. 146. 



- Entstehung d. Sexualzellen bei d. Hydromedusen. Jena 18S3 pag. 117. 



^ Zeit. Wiss. Z. 61. Bd. 1896 pag. 16] . 



