468 BULLETIN lOO, UNITED STATES NATIONAL MUSEUM. 



bearing a transverse series of 3 rather long, slender spines, and (2) 

 nonprominent plates with only 1 spine. Tube feet in 4 series, the 

 feet of the outermost series corresponding to the nonprominent plates. 

 Combined mouth plates produced actinally into a cone, the apex of 

 which is about the middle of median suture. Two suboral spines. 



HYMENASTERroES ZENOGNATHUS Fisher. 



Plate 127, figs. 4, 5 ; plate 128, fig. 2 ; plate 134, fig. 1. 

 Hymenasterides zenognathus Fishee, 1911o, p. 42.5. 



Diagnosis. — Paxillar area raised above the actinolateral membrane 

 which forms an even narrow border ; paxillae in 9 longitudinal series, 

 5, or laterally, as many as 7 spines to a paxilla, one being longer than 

 the rest; no visible muscle-fibers; scattered spiracula. Prominent 

 adambulacrals with 3 slender membrane invested sacculate spines; 

 nonprominent with one, each of which is opposite a tube foot of outer 

 series. Mouth plates conical actinally with 2 suborals, and 3 or 4 

 marginals. Fourteenth actinolateral spine the longest. E.=36 mm., 

 r=22 mm., R=1.64 r. Breadth of ray, over all, 21 to 25 mm.; of 

 paxillar area alone, 17 to 21 mm. 



Description. — The paxillar area is sharply defined from the lateral 

 fringe, or actinolateral membrane, which is interradially deeply in- 

 dented and follows the contour of the raised supradorsal membrane. 

 Thus the actinolateral membrane forms a narrow border of nearly 

 uniform width, and the spines do not project beyond the edge. They 

 are clearly visible, as the membrane is translucent. The supradorsal 

 membrane is thin and translucent, without visible muscle-fibers, and 

 with small, rather widely spaced, inconspicuous spiracula, which are 

 not in definite areas but sometimes form irregular lines. With the 

 exception of an interradial area they are pretty uniformly distributed 

 all over the membrane. Membrane everywhere rough with the points 

 of the paxillar spinelets, of which there are usually 5 (laterally some- 

 times 7) to a paxilla. The latter are in 9 quincuncial longitudinal 

 series. Each paxilla springs from a cruciform or f our-lobed base, the 

 lobes overlapping those of 4 other plates leaving quadrate or lozenge- 

 shaped papular areas. The pedicels are longest on the lateral paxillae ; 

 those of midradial series about half as long as the laterals, and the 

 spines, which are webbed, are in all cases longer than the pedicels. 

 One spine is usually longer and stouter than the others. The spines 

 are three-edged or triradiate in cross section. The papulae (1 to an 

 area) are attached to the pedicels. The valves guarding the osculum 

 have a truncate summit and are strengthened by about 12 spines, of 

 which the 5 or 6 median arc longest. About 8 other spines, much 

 shorter, form a comb just back of the valves, and are attached to the 

 same pedicel. The membrane at the base of the fans is pierced by 



