A FEW CCELENTERATES OF WOODS HOLL. IO5 



doubt genetically different from Zanclea. Briefly diagnosed, Zan- 

 clea was described by Gegenbaur as having four short oral lobes, 

 four radial canals and the same number of marginal tentacles, 

 the latter with numerous secondary appendages (Anhangen). 



In at least two aspects there are important differences in Gem- 

 maria, viz., the mouth is not marked by any distinguishable lobes 

 or lips ; and second, there are only two marginal tentacles. These 

 latter do not increase in number with age, so far as one may judge 

 by having them long under observation. This is likewise true of 

 Gemmaria implexa, taken by the writer at Naples, and described 

 briefly in a paper in the Naples Mittheilungen (Bd. XVI., p. 574). 



It would seem therefore that the genus Gemmaria of McCrady 

 must be recognized as founded on thoroughly good characters, and 

 that is it quite distinct from Zanclea of Gegenbaur. Hence we 

 must also accept McCrady's G. gemmosa as a distinct species, and 

 this name must entirely supplant that of Covynitis agassizii, as 

 pointed out in the preceding section. 



Colonies of the hydroid are quite frequently taken at Woods 

 Holl, and from a considerable variety of habitats, e. g., on shells 

 of Mytilis, Pecten, serpulid tubes, pebbles dredged from various 

 depths, pieces of waterlogged wood likewise dredged from similar 

 depths, and from floating Sargassum. In one particular, however, 

 there has been an interesting uniformity in every case which has 

 come to my notice, namely, the colonies are invariably associated 

 with encrusting polyzoa, usually Schizoporella or Membranipora, 

 and almost always with those colonies characterized by pinkish 

 or orange colored pigment, affording a background which re- 

 sembles very remarkably the color of the hydroid. The hydro- 

 rhiza forms an intricate network over the polyzoon, but so far as 

 I have been able to perceive there is no special evidence of mutu- 

 alism between the organisms. 



The following note concerning the peculiar nettling organs of 

 the medusae may not be amiss. The extension of the stalk 

 bearing the nettling organ is apparently brought about by a sort 

 of rotary, or oscillatory motion of the capsule, involving a spin- 

 ning-like operation by which the thread becomes extremely deli- 

 cate almost to the point of invisibility. After attaining its full 

 extension the capsule continues its motion for a variable time, 



