Notes on some Hydromedusae from the Bay of Naples. 577 



by McCrady ^ aud for wliich he established the geuiis, liad likewise 

 four tentacles. In 19U0 Mayer^ obtained a hydroid at the Tor- 

 tiigas which he described as the trophosome of the species, O. geni- 

 viosa^ the medusae of which when first liberated had but two ten- 

 tacles, nor did others appear. 



The question naturally arises, whether in these eases we may 

 bave a different species , or whether the medusae of the same species 

 uccasionally vary as to the number of tentacles. The latter seems 

 to me the more probable alternative. It is well known that me- 

 dusae of different species, or even of different genera, often resemble 

 each other so closely as to appear to be identica!. Hartlaub, for 

 iustance, as cited in a previous connection, has shown this to be 

 the case in several instances which need not be reviewed in this 

 connection. Such is apparently the case also with the medusae of 

 Gemmaria and Conjnifis. I am strongly convinced, however, that 

 in this case we bave to do, not with two distinct genera, but with 

 different species of the same genus; for it has never seemed to me 

 that there are differences between the two which are suffici ently 

 marked to justify generic distinction. And what is true in this case 

 is probably true in many others of similar sort. This is doubtless 

 due in large measure to the fact of the separate and independent 

 life of the two organisms, hydroid and medusa. When we shall bave 

 worked out critically the ontogeny of the several species, much of 

 the apparent anomaly will doubtless disappear. 



Corì/dendrium parasiticum Cavolini. 



Among the many species of hydromedusae which bave long 

 engaged the interest and observations of naturalists, few if any, 

 surpass the one bere under review. It was originally described by 

 Cavolini 3 in 1785 under the name of Sertidaria parasiUca in a 

 small monograph upon the Naples fauna, which for painstaking ob- 

 servations aud clear Interpretation may well rank as a classic of 

 its time. After its originai description it remained for nearly three 

 quarters of a Century little, if at ali known to students of the group, 

 though it is at present a fairly familiär object among its congeners 



1 Gymnophthalmata of Charleston Harbor. 1S57. 



2 Bull. Mus. Harvard Coli. Voi. 37 1900 pag. 35. 

 ^ Memorie Polypi Marini. Napoli 1785. 



