2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 9I 



The madreporite is situated on the sloping side of the disk just at 

 the edge of the abactinal surface. It is 2.5 mm in diameter and 

 about I mm high, with ahnost vertical sides. 



The rays are 15 in number (in both specimens) and are about 

 250 mm in length from the edge of the disk. The thickest and highest 

 portion, at the sixth or seventh adambulacral from the last marginal. 

 is 8 mm high and 8 mm broad, the ray here being evenly convex 

 abactinally. Just beyond the genital region the rays are 7 mm broad 

 and 5 mm high. 



The genital region of the rays is about 40 mm long. It is 

 only very moderately swollen and tapers gradually distally. It 

 is completely covered with small, lobed, overlapping plates elevated 

 in the center and bearing a small spine, more rarely two or three, 

 with many pedicellariae, and with papulae in the interstices between 

 the plates. Irregularly interspersed between the plates of the genital 

 region along the sides of the ray are a few larger plates bearing 

 longer spines. 



The costae in the proximal half of the genital region are irregular, 

 usually very short, and are scarcely to be distinguished from the 

 general plating of the area. They occur opposite every third adam- 

 bulacral plate. The few larger spines in this region are seen to be 

 more or less definitely associated with them. In the outer half of 

 the genital region the costae are in the form of narrow bands of 

 slightly elevated plates running across the arms, though scarcely 

 distinguishable in the median line. On either side of the arm they 

 bear from two to four spines, which are much longer than the spines 

 on the adjacent plates. There are nine costae in all in the genital 

 region, of which the first five are incomplete in varying degrees, the 

 first two being scarcely more than indicated above the adambulacrals. 



Beyond the genital region the dorsal plates abruptly become smaller 

 and wholly separated ; continuing to decrease in size, and also in 

 number, they disappear entirely after about 15 mm. Pedicellariae 

 in this area are excessively abundant, and they remain abundant to 

 the arm tips. Beyond the genital region there are two greatly re- 

 duced bands of plates representing costae. Just above every third 

 adambulacral beyond the genital region is a row of four stout plates, 

 each of which bears a long, slender, sharp spine ; the lowest of these 

 spines is the longest. 8 to 9 mm in length, the next two are almo.st 

 as long, and the uppermost, or fourth, is the shortest, much shorter 

 than the others. On the distal portion of the arms these combs of 

 spines become more widely spaced, occurring above every fourth, or 



