290 GEMMARIA IMPLEXA. 



Some time ago' I described the medusa of Alder's Coryne implexa, and afterwards" drew 

 attention to the fact that this medusa was in all essential points similar to that described by 

 M'Crady, whom I followed in referring the medusa to Gegenbaur's genus Zanclea. A more 

 careful comparison, however, has since convinced me that while the American and British forms 

 present no difference which could justify a generic separation from one another, they cannot be 

 referred to Zanclea, and must therefore receive the generic name of Gemmaria proposed pro- 

 visionally by M'Crady. 



In thus substituting the name of Gemmaria for that of Zanclea I find myself in accordance 

 with Mr. A. Agassiz, who has already recognised the difference between M'Crady 's and Gegen- 

 baur's medusae.^ Mr. A. Agassiz has also found in ]\Iassachusetts Bay another medusa which 

 he regards as a second American species of Gemmaria. Neither of the Amei'ican medusas, how- 

 ever, has been traced to its trophosome. 



Gemmaria implexa, Alder. 

 Plate VII. 



TuBULARiA IMPLEXA, — Alder, Catalogue Zooph., p. 18, pi. vii, figs. 3 — 6. 



Coryne pelagica, — Alder, Catal. Zooph., p. 13, pi. vii, figs. 1, 2. 



Coryne implexa, — Strethill Wright, Edin. New Phil. Journal. Alder, Suppl. Catal. 



Zooph., p. 3, pi. X, fig. 4. 

 Coryne Briareus, — Allman, in Ann. Nat. Hist, for July, 1859. 

 Zanclea implexa, — Allman, in Ann. Nat. Hist, for May, 1864, and June, 1864. 



Hincks, Brit. Hydr. Zooph., p. 59, pi. ix, fig. 3. 



TROPHOSOME. — Hyduocaulus consisting of simple or rarely branched offsetts 

 from a creeping net-like iitdrorhiza, springing at short intervals from the hydrorhiza, 

 and attaining a height of about half a hne ; pebisarc, for some distance from the 

 hydrorhiza, transversely corrugated and opaque, and then becoming abruptly trans- 

 parent and smooth, and forming a cup-like dilatation, which is separated by a 

 considerable interval from the contained coenosarc, and extends as far as the base of 

 the hydranth. Hydbanths, when extended, cylindrical, exceeding by many times the 

 hydrocaulus in length, when contracted thickly club-shaped ; tentacles numerous, 

 forty or fifty. 



' Notes on the Hydroid Zoophytes, in ' Ann. Nut. Hist.' for July, 1859. The hydroid is there 

 named Coryne Briareus. Wright and Alder, however, maintain its identity with the C implexa, Alder, 

 and though neither Alder's nor Wright's description will apply in all points to my hydroid, I prefer to 

 follow these zoologists in regarding the two hydroids as specifically identical, rather than run the risk 

 of further confusing the descriptive zoology of the Hydroida hy the retention of a doubtful species. 



°- • Ann. Nat. Hist.' for May, 1864. 



^ A. Agassiz, 'Illustrated Catal.,' p. 184. Hincks, however, does not recognise a generic difl'er- 

 euce between the Gemmaria of M'Crady and the Zanlcea of Gegenbuur. ' Brit. Hydr. Zooph.,' p. 59. 



