34 BULLETIN 16, UNITED STATES NATIONAL MUSEUM. 



spino. When dried the surface of plate shows often numerous minute bosses. 

 Directly above the actinolateral spine the specialized ridge narrows abruptly and 

 joins without a conspicuous break, that of superomarginal. The fasciolar channel 

 is several times broatler than the specialized ridge and is a V-shaped trough, on 

 whose sides are five to seven parallel superimposed but distinctly spaced series of 

 delicate spinelets in a continuous web. Each web extends from the upper end of 

 a superomarginal plate to the actinolateral spine. The whole apparatus of five 

 to seven webs or lamellae on either side of the V-shaped trough, extending over its 

 cavity, forms a very delicate cribriform organ or filter. The series of spinelets roof- 

 ing the furrow are much flattened and the tip ends m several minute points. Owing 

 to^the greater width of furrow, these spinelets are much longer than those of lower 

 end of inferomarginals. The other spinelets are narrow and more deHcate and 

 decrease in size in each successive tier toward bottom of furrow. In alcoholic 

 specimens the membrane investing the spinelets is usually so thick that they are 

 only seen with difficulty. The spinelets act only as a support for the membrane 

 ami do not themselves function as strainers, as in Astropeden. The superomarginal 

 spine which stands at the top of the plate is either terete, tapering, and pointed, 

 or broadly lanceolate and acute like a spear tip. On outer part of ray there are 

 sometimes two spines on a few plates. 



The variation in number of marginal plates has already been indicated in the 

 table. The margin of ray and disk is thicker in some examples than in others, the 

 appearance being heightened by recurved rays, when the actinolateral angle is 

 rounder and less abrupt. The exposed surface of the specialized ridge of supero- 

 marginal plates is thin or narrow, but varies more or less, being slightly broader in 

 four Atlantic specimens; but in another Atlantic example from off Newfoundland 

 they are as narrow as in Alaskan specimens. The height of superomarginals is 

 variable, specimens from 1,033 fathoms having much lower ones. This is readily 

 appreciated by noting the distance between the two series of marginal spines in 

 the interbrachial arc. 



Actinal surface. — The adambulacral armature is essentially alike in both 

 Atlantic and Pacific specimens, some examples showing a preponderance of three 

 or four furrow spines, others of four and five. Besides the spine (not of furrow 

 scries) which usually stands on the outer aboral corner, there is usually one to 

 several very much smaller and more delicate spinelets along adoral and outer edge 

 of plate. These can not be distinguished readily unless specimen is dry. 



Actinal interradial areas, like marginal and adambulacral plates, are overlaid 

 by membrane through which the plates are scarcely visible until dried. Plates 

 are arranged in series running from marginals to adambulacrals. Deep channels 

 also fallow same course. These are overhung by a series of spinelets embedded in 

 membrane, being a continuation of the marginal fascioles. The interradial channel 

 splits and runs on either side of mouth plates. The first on ray always runs between 

 second and third adambulacral, the second between the third and fourth, and so 

 on. The photographic figure will show the arrangement of plates. 



Anatoraical notes. — No intestine, no intestinal coecum, no anus. The conical 

 eminence in center of disk contains a prolongation of the ccelom and is divided by a 

 vertical septum. Stomach large, single, firmly moored to abactinal waU. Hepatic 



