114 



Genus llymenosoma, Leach. 



Hymenosoma rostratum, Haswell, Cat. Aiist. Crust, p. 116. 



PI. iii. , figs. -2, 2rt, 26. 



The following notes are to be taken in addition to the 

 description in the above catalogue. 



The surface of the carapace is sometimes convex, some- 

 times quite flat, or even sunken. The spines or teeth at the 

 lateral angles are sometimes very strongly developed. The 

 margin is raised and thickened, and the antero-lateral margin 

 behind the post-ocular spine, which curves towards the eye, 

 has a slight prominence. In the male the posterior margin is 

 very short and arcuate. 



The rostrum is about one-fourth the greatest breadth of 

 the carapace, elongate, triangular, and fiat above, it is strongly 

 keeled below, the keel produced to a septum between the an- 

 tennules, with its greatest depth just anterior to them. 



The ocular peduncles project about half the length of 

 the rostrum ; there is a conical tooth beneath on the orbital 

 border at the base of the peduncle, and a small tubercle on 

 the peduncle close to the ophthalamus on the anterior side. 



The epistome is rather long and full. 



The anterior angles of the buccal frame are very promi- 

 nent. 



Of the three pterygostomial tubercles the middle one is 

 slenderer and more spiniform. 



The orbito-fossettes are very poorly developed. 



The antennules are robust, and when extended reach 

 beyond the rostrum. 



The antennas are slender and only reach a little beyond 

 the eyes. 



The merus of the external maxillipeds has the follow- 

 ing joint articulated near the prominent and rounded exter- 

 nal angle, and there is a slight notch at its base. 



On the acute upper margin of the merus of the cheliped 

 there is a short keel-like prom.inence near the proximal end, 

 and the palm is well keeled on both its upper and lower 

 margins. 



The dactyli of the ambulatory legs are about three- 

 fourths the length of the propodi; they are slightly curved 

 and carry a series of small teeth of about equal size with 

 hairs between. 



A small species, not exceeding in size the EJamcna trun- 

 cata. 



