CLASSIFICATION. 



47 



7. Genns. — Culcita, Agass. 



Body pentagonal^ with a thick, blunt border, which forms a very high side-area, with- 

 out plates at the margin. Body covered Avith granules, and fissured at the angles ; valve- 

 like and pincers-like pedicellariee ; vent subcentral. 



8. Genns. — Astkuiscus, Luid. = Asferhia, Nardo ; T'almipes, Linck. 



Body pentagonal, with short rays ; under surface flat, upper surface more or less inflated 

 or completely depressed, thin and membranous at the border, without plates. Ossicula on 

 the under side covered with small, pointed, or blunt, or cylindrical spines, which stand 

 either simply on each plate, or comb-like in rows. The plates on the upper surface covered 

 with similar processes, either comb-like or fasciculated ; single pores between the plates of 

 the upper surface of the disc and of the rays. The pores cease, sooner or later, near the 

 margin ; vent subcentral. 



9. Genus. — Pteraster, M. and T. 



In form it resembles the genus Aslerincits, with two rows of tentacula in the ambu- 

 lacral avenues, and a central vent. 

 The upper surface of the disc and rays 

 is completely covered with a naked 

 skin, from which tufts of small spines 

 are regularly developed, and supported 

 upon the osseous network of the ray. 

 The border is armed with a series of 

 longer spines, united together up to 

 their extremities by a fold of the tegu- 

 mentary membrane. The under side 

 of the ray is provided with a series of transverse spines, formed into fan-like structures by 

 folds of the skin, and superimposed on each other along the sides of the avenues ; there 

 are no pedicellarise. 



Fig. 23. 



A. 



A portion of a ray of Pteraster miHtaris, M. and T. 

 A, the under ; B, the upper surface. 



