354 L. MURBAOfl. 



Corynitis Agassizii, McCrady, and its Medusa, Gemmaria. 



Last summer, while examining some sargassum driven into 

 Vineyard Sound from the Gulf Stream, I found a small polyp 

 which proved to be Corynitis Agassizii, McCrady. In his 

 description of Halocharis (Corynitis), Agassiz ^ says the 

 medusoid stage was not found, but later he found his Halo- 

 charis identical with Corynitis of McCrady, who had observed 

 the medusae. But according to Allman- the medusa as- 

 cribed to Corynitis by both McCrady and Agassiz has four 

 marginal tentacles, each with a clavate extremity beset by 

 nodulated pads of thread-cells, and " four overarched spaces 

 between the roots of the radiating canals," while the immature 

 medusa possesses only two tentacles and no " overarched 

 spaces.^' Allman accepts the general correctness of McCrady's 

 observations with some reservation, pointing out that McCrady 

 captured his four-tentacled medusa in the open sea. He, 

 therefore, has inferred its relationship to Corynitis by inter- 

 mediate stages. 



As my polyps possessed numerous medusa buds, they were 

 kept under observation to determine the question raised by 

 Allman, and finding no previous record of the occurrence of 

 Corynitis in the vicinity of Wood^s Holl, 1 append a short 

 description of the polyps to better establish their identity, and 

 to add a few new points. 



They are found most abundant on Membranipora incrusta- 

 tions below the low water mark, probably because on the 

 reddish calcareous deposit they have very good colour protec- 

 tion, as is evident from the difficulty of readily seeing them. 



The hydrorhiza is deep pink, while the tiny hydranths have 

 a delicate, translucent, white shade enveloping body and ten- 

 tacles, with pink between the lighter edges. The hydrorhiza 

 is slender and thread-like, and anastomoses frequently, form- 



' Agassiz, L., ' Coutr. Nat. Hist. U.S.,' vol. iv, pp. 239, 240, 1862. 

 ' Allman, G. J., ' A Monograph of the Gymnoblastic or Tubularian Hy- 

 droids,' p. 286, 1870-72. 



