448 BULLETIIsr 100, UNITED STATES NATIONAL MUSEUM. 



4 times the length of the pedicel. There are 2 to 5 or 6 prominent 

 papulae to each mesh. The primary plates have 4 slender lobes, 

 which are connected to neighboring plates by upward of 4 or 5 ellip- 

 tical overlapping ossicles, forming slender trabeculae. The meshes 

 are not symmetrical and often several are confluent, especially on 

 outer part of ray. 



Marginal plates 24 or 25 prominent, with compressed pedicel bear- 

 ing 50 or more very delicate spines which are decidedly longer at the 

 lower end of the pedicel than at the upper, being 1^ to 1^ times the 

 width of the pedicel. The marginal spines are also shorter than the 

 central, as in the case of the abactinal plates. Between 2 marginal 

 plates are 1 to 3 small abactinal paxillae. The marginals define the 

 ambitus on the ray, but at the base pass to the actinal surface, keeping 

 close to the adambulacral plates in consequence of the small size of 

 the actinal intermediate areas. 



Furrow spines very slender, 10 on the first plate, then 9, then 8 

 or 9, and on the outer part of the ray, 6, The median spines are 

 longest and about 1^ to 2 times as long as the base line of comb, 

 while the later almost are commonly only one-half as long as the base 

 line, the intermediates being graduated in length between the two. 

 They are united for about one-third their length by membrane. On 

 the surface of the plate is an oblique, arcuate, transverse comb of 

 7 to 9, usually 8 or 9, slender, basally webbed spines, the inner 5 or 6 

 subequal and about 1^ to 1^ the length of the median furrow spines, 

 but slightly stouter, the outer 2 or 3 considerably and progressively 

 shorter. The spines are borne on an elongate slightly crescentic 

 tumidity of the plate, the inner end of which is at the aboral furrow 

 corner of the plate and the outer near the outer adoral corner. 

 When the spines are spread fanwise with the points adorad (instead 

 of being bent aborad and obliquely away from furrow) the base of 

 the comb is nearly a semicircle and the special ridge has the appear- 

 ance of a low pedicel comparable to the marginal pedicels but much 

 less conspicuous. 



Mouth plates with 15 slender, marginal spines united basally by 

 a web, and increasing in length from the outer toward the inner end 

 of the plate, the innermost spine being as long as the base line of 

 the marginal series. Suboral spines about 13, in a zigzag series the 

 length of plate, basally webbed, and when standing erect forming a 

 rather dense group on the companion plates, the ends of the spines 

 rising well above the marginals (except the innermost to which the 

 suborals are nearly equal). The spines, when separated, seem to 

 form 3 oblique transverse series from the median suture aborad 

 toward the margin. 



Madreporic body situated a little nearer margin than middle of 

 r, and with a large paxilla on the adcentral side. 



