260 PROF. p. M. DTJNCAJf S EEVISIOK OF THE 



and rather deep groove extending from the apex to the peri- 

 stome ; posteriorly there is a decided beak, above which is the 

 periproct, circular in outline, and situated in the posterior 

 truncation. 



Apical system excentric in front ; there are four basal plates, 

 and they are perforated by the generative ducts ; the madrepo- 

 rite is in the usual basal, and it passes backwards between the 

 posterior basals and radials into the posterior interradium. 



The ambulacra dissimilar ; the anterior is sunken, and there is 

 a pair of minute pores to each of its plates. The other ambu- 

 lacra are subpetaloid, not closing, and in very slight grooves. 

 The antero-lateral are the shortest and are nearly transverse ; 

 and in all the poriferous zones are wide, the pores being 

 unequal, and the interporiferous areas being very narrow. The 

 exceedingly shallow ambulacra are almost devoid of tubercles. 



The iuterradia are unequal, the posterior being the narrowest; 

 there are a few large primary tubercles in each within the peri- 

 petalous fasciole ; elsewhere the ornamentation is of rows of 

 large granules, but it is largest on the keel and the extremity 

 of the beak. 



Peristome excentric in front, semi-lunar, broader than long, 

 with a small posterior lip. Periproct small, circular, many- 

 plated, just above the plates surrounding the upper part of the 

 beak. Beak blunt, slanting from below upwards, and with a 

 comparatively level upper surface. 



Subanal fasciole surrounding the base of the keel, ovoid, 

 with the point downwards. Peripetalous fasciole oblique, narrow 

 and extending across the ends of the ambulacra and cutting across 

 the anterior groove far above the peristome. The sternum arched 

 and keeled. The tubercles within the fascicles carry long curved 

 spines, elsewhere they are shorter, except on the sternum. 



Hecent. Arafura Sea, 800 fathoms. 



Alex. Agassiz, in his description of the genus, remarks that the 

 genus forms a transition between his Brissina and the Pourta- 

 lesiidse. The groove of the anterior ambulacrum is far less marked 

 than in the Pourtalesiidse. The actinal surface is not flattened as 

 in the last-mentioned family, but arched. The arrangement of 

 the tubercles in the interradia within the peripetalous fasciole js 

 like that of some species of Mefalia. 



The genus Tuheraster, 1885, Peron et Gauthier, Ech. foss. de 



