48 THE OCEANIC HYDROZOA. 



small aperture of the nectosac, surrounded by a five-toothed raised margin. Posteriorly, 

 the inferior face slopes very obliquely upwards and backwards, and presents a triangular 

 space entirely occupied by the aperture of the hydroecium. 



The hydroecium is bell-shaped and very large, occupying nearly the whole length of the 

 organ. Its inferior aperture is narrow from side to side, but measured antero-posteriorly it 

 equals about half the diameter of the nectocalyx in this direction. 



The somatocyst — a large oval sac, occupying nearly all the space left between the 

 posterior wall of the hydroecium and the posterior contour of the organ — gives off no cseca. 

 Its walls are highly vacuolated, and the duct by which it communicates with the coenosarc 

 opens into its apex. 



The nectosac, finally, is subcylindrical, and tapers above to a point, against which 

 the nectocalycine duct applies itself. 



The distal nectocalyx (PI. Ill, fig. 1 c) is pyramidal. Five more or less prominent 

 longitudinal crests mark the outer surface of the organ, and are produced at its lower 

 extremity into as many serrated points. The posterior of these is directed downwards and 

 backwards ; the lateral ones are curved sharply inwards ; and the anterior pair pass down- 

 wards and forwards. Of these last that on the right-hand side is produced forwards into a 

 crest which almost immediately becomes confounded with a large serrated perpendicular 

 plate, which traverses the anterior face of the organ, and gives off from its inner surface a 

 transverse plate, deeply toothed on its free edge. 



The left-hand anterior point is prolonged upwards as a slight ridge for some distance, 

 and then rises into a very strongly serrated vertical plate, which is overlapped by the 

 transverse plate of the other side — the two enclosing the hydroecial canal. Arrived at the 

 conical, superior portion of the organ, the two crests diminish in height and become obsolete. 



The nectosac is hardly more than two thirds as long as the whole organ, sub- 

 C5'lindrical, and rounded above. The nectocalycine duct abuts against its apex. 



The hydrophyllium is cuboidal, but narrower behind than in front, where it is somewhat 

 excavated. The phyllocyst is oval, and two curved, narrow cseca proceed from it above. 



Length of the proximal nectocalyx . . ^ inch. 



Length of the distal nectocalyx . • ? „ nearly. 



A single specimen of this species was taken in Torres Straits, off the south-east coast of 

 New Guinea, on the 24th of July, 1849 ; but I observed it neither before nor afterwards. 



The coenosarc was imperfect and its appendages incompletely developed. The hydro- 

 phyllium described and figured was detached, but I have no doubt it belonged to this 

 specimen. Its resemblance to the AmpMroa data described below is so striking, that I 

 imagine the latter must be the Diphyozooid of Abyla trigoria. 



It is with some little hesitation that I identify this species with the Ahyla trigona of 

 Quoy and Gaimard, described and figured in the .' Annales des Sciences' for 1827, and 

 subsequently in the 'Zoology of the Voyage of the Astrolabe,' t. iv, p. 87, pi. 3, iv, figs. 

 12—17; but there are so many points of similarity that I prefer to run the risk of making 

 a species too few rather than one too many. 



