48 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Superomarginal plates 42 to a ray, the last 10 or 11 on each side 

 of a ray in contact medially, and not corresponding plate to plate, 

 but sometimes alternating. Beyond the interbrachial arcs the plates 

 encroach more and more upon the abactinal area as the extremity 

 of ray is approached, so that from being proximally higher than 

 wide they become wider than high. The general surface of the 

 plate is covered with smooth skin and each hears on the rounded 

 angle between the dorsal and lateral face a short, sharp, slightly 

 compressed, conical spine. A similar spine occurs in a correspond- 

 ing position on each iaferomarginal. Proximally the vertical fas- 

 ciolar grooves (continuous between both supero- and inferomarginal 

 plates) are wider than the elevated ridge separating them, but be- 

 come narrower toward the end of the ray. The margin of ihe ele- 

 vated ridge is provided with a series of numerous delicate spinelets 

 entirely immersed in a web, which continues uninterrupted to the 

 adambulacrul plates, roofing over the channels between the consecu- 

 tive double series of actinal intermediate plates. Tlie grooves be- 

 tw^een the marginal plates are closely packed with delicate spinelets 

 ni quincunx, these being visible at base of ray, and fonning si)ecial- 

 ized cribriform organs wider than the naked ridge separating suc- 

 cessive grooves. But these cribriform organs, along with the groove 

 containing them, become narrower and narrower toward the end of 

 ray, and beyond the midde of ray are entirely roofed over by the 

 peripheral web. The cribriform organs are slightly wider at the 

 top than at the lower end, and contain about 16 vertical rows of un- 

 webbed spinelets. On the inferomarginal series, the organ, which is 

 absolutely the same and continuous with that of the superomarginal, 

 narrows quickly and ends at the ventrolateral angle of the ray. 

 Proceeding along the ray the organs become closed over by the 

 peripheral roofing web somewhat sooner than do the superomarginal 

 fascioles. The exposed surface of the cribriform organs forms a 

 shallow V-shaped channel paved by the tips of the spinelets. 



The lateral face of the inferomarginal (between the ventrolateral 

 spine and dorsal suture) is proximally about two-thirds as high as 

 that of the corresponding superomarginal, but beyond basal third of 

 ray becomes nearly or quite equal. There is a slight depression 

 marking the suture between the two series of marginals, but no 

 fascicle, the membrane being continuous. The actinal surface of 

 inferomarginals is proximally slightly wider than high and sub- 

 equal distally. The cribriform organs end abruptl}'^ at the ventro- 

 lateral angle, the channels between that point and the furroAV being 

 shallow, and covered by the webbed spinelets only. Terminal plate 

 broadly obovoid, depressed, with sometimes a spine on ventrolateral 

 corner. 



