52 BULLETIN" 100^ UNITED STATES NATIONAL MUSEUM. 



channels covered only by the webs, to the timbiilacral furrow. The 

 spinelets supporting the webs on actinal surface are much coarser 

 than those of lateral surface. Supporting ihe web along one side of 

 an interradial superomarginal are about 30 spinelets, and of the cor- 

 responding inferomarginal as far as the spine, about 15. The odd 

 interradial plates are just like the others. Terminal plate triangu- 

 lar as seen from above, with five short spines on the broad distal 

 end. In a young specimen these are relatively much longer and 

 protect the terminal tentacle. 



Actinal intermediate plates extend to thirteenth inferomarginal; 

 but beyond the fifth there is only a single longitudinal series. Each 

 double transverse series corresponds accurately to an inferomarginal, 

 that opposite the odd plate meeting the mouth plate and first or first 

 and second adambulacrals. There are eight plates in each row of 

 the odd interradial duplicate series. Surface of plates smooth, 

 covered by thin membrane. There are ordinarily 5 to 7 spinelets on 

 the margin of each plate that borders a fimbriated channel. From 

 the inner or coelomic side the plates are seen to be strongly imbri- 

 cated, the free edge being that toward margin. 



Adambulacral plates with an angular furrow margin, the apex of 

 which is nearly in the center of plate beyond middle of R, but moves 

 toward the adoral edge of plate as the mouth is approached, until on 

 the first 5 or 6 plates the apex is so near the adoral side of plate 

 that the free margin is quite oblique, as in Goniopecten. The furrow 

 margin be^rs, on the first (compressed) plate 6 to 8 spines, on the 

 rest 10 or 11, basally webbed; they are rather long, close-set, blunt, or 

 dully pointed, and the longest spine is on the apex of the angle, the 

 rest becoming gradually and markedly shorter toward either end of 

 series. The groups tend to meet across the furrow and segregate 

 consecutive pairs of tube feet. At the base of ray, about 10 plates 

 are free from the actinal plates and bear a marginal series of 6 to 8 

 stout spinelets webbed for about half their length. One or 2 of these 

 on the aboral edge of plate become gradually enlarged. Beyond the 

 tenth plate one outstrips the other, forms a specialized sharp sub- 

 ambulacral spine, similar to but slightly larger than the nearest in- 

 feromarginal spine. Far along ray the furrow spines decrease rap- 

 idly in size, while the subambulacral spine decreases slowly, so that 

 there the discrepancy in size between the two is greatest, the subam- 

 bulacral being the longer; proximally the reverse is true. 



Mouth plates prominent actinally and very similar to those of 

 Goniopecten. The plates are interradially long and narrow. The 

 furrow series consists of 8 or 9 small spines, similar to but shorter 

 than those of the first adambulacral, there being a slight angle in the 

 series near inner end of plate. Two or 3 irregular scries of much 

 heavier, short, pointed spines occupy the sloping surface of each 



