444 PROCEEDINGS OF THE NATIONAL MUSEUM vou 80 



arm base there may be as man}' as 6 or 7 spinules, and in the distal 

 portion of the genital region the number is usually one. Though 

 commonly irregularly grouped, these spinules show a tendency to 

 become aligned in a transverse row. On the surface of the plates 

 in the vicinity of the spinules are more or less numerous very small 

 pedicellariae resembling those on the disk. 



The delicate membrane covering the abactmal surface of the arms 

 beyond the genital region carries numerous scattered pedicellariae 

 resembling those on the disk. These seem to have no regular arrange- 

 ment. 



The actinostome is 6.3 mm in diameter. The mouth plates are 

 triangular, with the interradial (longest) apposed sides straight, the 

 aboral side obtusely notched, and the radial side obtusely angled 

 where the actinostome joins the ambulacral groove. The actinostomal 

 border bears 3 subequal slender spines. Just beyond these, at the 

 junction of the actinostome and the ambulacral groove, is a small 

 lobate projection of the mouth plate on w^hich are situated 2 (rarely 

 3) spines, the one next to the ambulacral groove resembling the 

 spines just noticed, the other (or others) smaller. Near the distal 

 end of the plate on the side adjoining the ambulacral groove are 2 

 (rarely 3) additional spines smaller than those previously mentioned 

 and situated at some distance from them. In about the middle of 

 the mouth plate, halfway between the long interradial side and the 

 opposite angle, is a large stout spine roughly twice as long as the 

 others mentioned, and between this and the outer angle of the plate 

 adjoining the ambulacral groove is another spine, about two-thirds 

 its size. Near the angle between the long interradial side and the 

 distal margin of the mouth plate there may be another small spine. 

 All the spines are enclosed in skin sacks, which bear numerous very 

 small pedicellariae. 



The first adambulacral plates are about half again as broad as 

 long, the second are somewhat longer than their median width, and 

 those following increase in length, those in the genital region be- 

 ing somewhat longer than the width of the proximal end or slightly 

 longer, and the outer being about twice as long as the width of the 

 proximal end or even longer. All are strongly concave on the side 

 toward the ambulacral gi'oove. The ambulacral groove, which at 

 first is rather broad, narrows distally, the adambulacrals finally 

 meeting in the midline so that the tube feet are arranged in widely 

 separated pairs. 



The first two adambulacral plates are united by a syzygy with 

 a small ligament mass visible halfway between the median line and 

 the border of the ambulacral groove. 



