A CASTA SPORILLUS. 319 



basal edge in consequence crenated ; the ribs are either placed at an 

 unusual distance from each other, and consequently are few in number, 

 or are pretty close together. The edge of the basal cup is either quite 

 smooth, or closely crenated, or distantly toothed, in conformity with 

 the state of the internal surface of the parietes. The radii have nearly 

 smooth edges, with their summits more or less oblique. They some- 

 times extend down only three fourths, or only two thirds, of the length 

 of the shell, and the margins of the parietes under the radii being a 

 little hollowed out, the sutures are converted into clefts or apertures 

 (of course covered by membrane) like, but not so large as, those in 

 A . fenestrata. The margins of the parietes are hollowed out only on 

 the side of the radius, and not on both sides of the sutures, as is most 

 usual in A. fenestrata. In some specimens the radii extended down 

 close to the basal cup, and only very minute clefts were left between 

 the opposed edges of the parietes. 



In the animal's body the only noticeable character was, that on the 

 anterior ramus of the fourth pair of cirri, some of the segments were 

 furnished with very broad and thick, small, downwardly curved, teeth 

 or hooks, like those described in certain varieties of A. sulcata ; but 

 they are here stronger and thicker. The segments in the three pos- 

 terior pairs of cirri are not so much elongated, as in the other species. 



9. Acasta sporillus. PI. 9, fig. 9 a — 9 d. 



Shell purplish-brown, with the parietes internally strongly 

 ribbed and reticulated : carino-lateral compartments ex- 

 tremely narrow, not extending down to the basis. 



Uab. — Sooloo Islands, East Indian Archipelago ; Mus. Dana. 



I am indebted to Mr. Dana, the distinguished naturalist 

 of the United States Antarctic Expedition, for two speci- 

 mens of this interesting species, which, in the singular reti- 

 culated structure of the inner surface of the walls, and in 

 the almost rudimentary condition of the carino-lateral com- 

 partments, not extending down to the basal cup, is very 

 distinct from the foregoing species. I have used Mr. Dana's 

 very appropriate MS. name of sporillus. The specimens 

 were dredged up, lying quite loose and unattached at the 

 bottom of the Sooloo sea ; the one which I opened, must 

 have long lain dead; but Mr. Dana assures me that some 

 were living, and he has sent me drawings of parts of the 

 mouth and cirri : I am much surprised at this circumstance ; 



