ASTRO PYGA EADIATA. 421 



one principal vertical row of secondaries extending to the abactinal system, 

 this primary row being flanked interiorly near the abactinal system by a 

 short parallel row of secondaries, and by an interior row of small tubercles 

 near ambitus. The coronal plates are narrow, elongate ; the median inter- 

 ambulacral space near ambitus contained between the narrow bare forks of 

 the median ambulacra! space, which extends to ambitus, is triangular, filled 

 by diagonal rows of primary tubercles, forming also very irregular horizontal 

 rows of uniform size, somewhat smaller towards median line. The tubercles 

 of both areas are small, very distinctly crenulated, with a broad flat scrobicu- 

 lar circle, sharply marked, slightly raised above the general level of the 

 test The spines are extremely slender and short compared to the great 

 diameter of the test in the other species of this family. They are 

 either uniformly colored or variegated, as in true Diadema, by transverse 

 bands of lighter color. The abactinal system is large ; anal plates elon- 

 gate, triangular ; madreporic genital slightly larger than the others ; geni- 

 tal openings close to apex, separated by narrow rectangular ocular plates 

 adjoining the large anal area ; base of anal membrane strengthened by a few 

 concentric rows of irregularly shaped plates, decreasing rapidly in size, carry- 

 ing very diminutive spines like those of the anal edge of the genital plates. 



in a small specimen the ambulacra are quite gibbous near edge, the 

 outline is very pentagonal ; the tubercles forming only vertical and not 

 diagonal rows in the median interambulacral space (six rows). The actinal 

 part of the test is not so extremely flattened, nor is it thickly covered by 

 tubercles as in large specimens ; the actinostome of course is very large, 

 compared to the diameter of the test ; the poriferous zone is of uniform 

 width, the tubercles proportionally much larger ; the pits extending along the 

 sides of the bare median interambulacral space are well marked. Nothing 

 special in the abactinal system, except somewhat less pointed genital plates. 



The color of this species when alive, Peters says, is whitish-green mixed 

 with reddish-brown. The anal system, genital plates, and bare median inter- 

 ambulacra are reddish, with a row of sky-blue spots placed in the pits of the 

 coronal plates; a similar spot is found upon four of the genital plates, a large 

 number of similar spots on the actinal membrane. Spines reddish-brown 

 ringed with greenish-white. The dried specimens I have examined are of 

 various tints, from a nearly uniform greenish-white test to a uniform dirty 

 violet color, the bare median interambulacral spaces being either lighter 

 or darker than the rest of the test. 



