CLARK : NEW GENERA OF ECHINODERMS 119 



being very small; two of the very small rays alternate between the 

 three of full size; the other three are side by side between two of the 

 later. 



The gonads extend to the ninth superomarginal. 



The interbrachial septum is very deep, extending from the stomach 

 to "the lateral interradial body wall, and is membranous except for a 

 broad centrally situated pillar composed of large overlapping plates. 



Prominent superambulacral plates are present. 



The pedicels are in two rows; they carry large sucking disks and are 

 connected internally with double ampullae. 



The plates of the abactinal surface are very numerous, greatly re- 

 duced in size, narrow, crescentic with swollen and rounded ends, im- 

 bricating outward in the median line and perpendicularly to the mid- 

 radial line elsewhere. Three parallel rows of larger plates occupy the 

 mid-dorsal line of the arms; from the outer of these on either side the 

 smaller plates extend in regular diagonal rows to the superomarginals, 

 in such a maimer that the diagonal rows arising at any one point in 

 the median line run both distally and proximally at the same angle with 

 the superomarginals, while the plates of the succeeding rows also form 

 straight and regular transverse rows between, and perpendicular to, the 

 mid-dorsal rows and the superomarginals with which, however, they 

 do not quite coincide. 



Externally the lateral plates appear as crescents regularly decreasing 

 in size from the dorsal region to the margin, each crescent partially 

 surrounding a single large papula situated in its concavity, on its 

 abactinal side; the plates of the median rows, while commonly crescentic 

 with the concavity proximal, may be triangular or irregular in shape. 

 The plates of the disk are irregular; most of them are of about the same 

 size as the median plates of the arms, but they become smaller about the 

 anal opening. 



To the naked eye the appearance of the abactinal skeleton is some- 

 what similar to that in such species of Henricia as H. leviuscula, though 

 the arrangement of the plates is much more regular. 



The surface of the abactinal plates is thickly beset with numerous 

 fine spines, of which the larger may bear from 20 to 25. In the proxi- 

 mal third to half these spines are stout, rounded-conical, with a dull 

 surface, but the distal portion is glassy and transparent, in lateral 

 view increasing in diameter at first slowly, later more rapidly, to the 

 coarsely serrate tip, so that they appear narrowly fan-shaped; in end 

 view they are seen to consist of three very delicate glassy calcareous 

 laminae united by their inner edges. 



The papulae are large and conspicuous, decreasing in size from the 

 mid-dorsal region of the arms to the superomarginals; they are arranged 

 in very regular diagonal, and also transverse, rows. They are absent 

 from the region between the central portion of the disk and patches 

 at the base of the arms, and from a region including the actinal half of 

 each interbrachial angle and extending thence in a long triangle to 

 about the eighteenth inferomarginal. On the arms there is one papula 



