418 ASTROPYGA PULVINATA. 



zone is broader than in Diadema, nearly as broad as the median ambu- 

 lacra] space ; the pores are arranged in four irregular vertical rows forming 

 steps of pores of three and one pair. The genital plates and abactinal 

 system, with the exception of the plated anal system, not materially differ- 

 ent from Diadema. Actinal membrane thickly covered by minute elliptical 

 or rectangular plates, with a few larger plates carrying spines irregularly 

 scattered. The jaws much smaller, in proportion to size of test, than any 

 other genus of Diadcmatidae. Coronal plates of actinal surface and near 

 ambitus deeply pitted when seen from inside of test, the pits corresponding 

 to the primary tubercles. 



Astropyga pulvinata 



! Cidarites pulvinata T.amk., lSlfi, An. s. Vert, 



I Astropyga pulrinatn Ahass., ink;. ( '. U. Ann. Sc. Xat.. VI. 



PL IIP./ 4; PL IIP./. 4-5. 



This species has a more globular, less depressed test than A. radiata, with 

 broader bare median interambulacral spaces. It can at once lie distinguished 

 from its congener by the shape of the genital plates, which form nearly equi- 

 lateral triangles, with large genital openings, and correspondingly larger 

 rectangular ocular plates: the anal system also is surrounded by an exterior 

 row of much larger plates, the structure of the whole abactinal system 

 being in striking contrast to that of A. radiata. with its elongate lanceolate 

 genital plates, and diminutive plates surrounding the anal system. The 

 coronal plates are proportionally high, specimens of the two species of the 

 same size in the Jardin des Plantes having thirteen plates only in A. pulvi- 

 nata, while there are nineteen in A. radiata. The size of the primary tuber- 

 cles is correspondingly larger, and the number of vertical rows less ; speci- 

 mens of same size showing eighteen rows at ambitus in radiata and only 

 fourteen in pulvinata. The spines are also stouter, more coarsely striated, 

 with more marked verticillations ; the peculiar flat raised scrobicular circle, 

 so characteristic of A. radiata. is replaced in this species by a gradually rising 

 mammary boss, indistinctly defined at the base. The bare median interam- 

 bulacral space covers nearly the whole of the test above the ambitus, there 

 being but a small triangular part of the test near the ambitus covered by 

 primary tubercles, forming short vertical rows. The actinal part of the test 

 is much less flattened than in A. radiata. the tubercles less crowded upon 

 it, with larger and more numerous secondaries ; while above the ambitus, 



