2g BULLETIN 70. UNITED STATES NATIONAL MUSEUM. 



Terminal plate, seen from side, is about as long as last two superomarginals, 

 and is strongly coneave on side toward abactinal membrane. There are five, some- 

 times six, prominent spinules, subtubereular and eonical; of these one (rarely two) 

 is on the extreme tip. one at either side of the end of ambidacral furrow just below 

 the terminal spinule, and one on either side, abactinal m i)osition. In Alaskan 

 specimens there are only three spinules on terminal plate, those mentioned last 



being absent. 



The inferomarginal i)lates are longer than high, and correspond to supero- 

 mar.'inals in number; or there may be one more; they are not always exactly 

 opposite plates of upper series. They do not extend onto actinal surface but are 

 confined to side waU of ray. Inferomarginals lack spines or any special armature 

 except the three cribriform" organs shared with the superomarginals. 



There are always three cribiiform organs to each interbrachial arc. Of these 

 the median is slightly the largest, having twenty to twenty-four lamella;. These 

 lamella; are made up of a linear, perpendicular series of flat spinelets or oblong 

 platelets in a thin web-like investment. More or less of the spinelets are free 

 around the edges, especially the actinal. Each organ has a slight depression down 

 the center. 



Adambulacral jjlates are narrow and rather long, conspicuously excavated 

 on furrow margin. Adoral end is most prominent and is surmounted by one 

 or two sharp tapering spinelets, one slightly compressed and curved, being directed 

 into the furrow; the other, usually a trifle smaller, is either reflected back over 

 the plate or is turned aborad. The latter is frequently absent. Midway between 

 the extremities of plate is a rather small valve-hke, scoop-shaped scale, resembling 

 one-half of a valvate pedicellaria — the "segmental papilla." It is articulated 

 to plate, on edge of furrow by a straiglit base, and the free edge is broad and rounded. 

 It closes over a small slit in the plate, which is absent beyond basal fourth of ray. 

 The valve beyond the proximal third to two-thirds becomes transformed into a 

 small lanceolate spine let, so that there are either two or three spinelets to each 

 plate beyond this point. Alaskan specimens, which are smaller than those from 

 California, usually have only one regular spinelet, and the segmental ])apill8e extend 

 rather farther along ray. 



Mouth plates very prominent, the united pair fonning a broad keel, with a wide 

 lanceolate median suture, the companion plates touching at the inner and outer 

 ends. The inner extremity of the combined pair is roimded and bears a single 

 short, conical spinule (frequently absent from being rubbed ofl') ; and on margin, 

 nearer peristome, on either side, is a curved compressed, smaller spinelet. Between 

 latter and first adambulacral plate are two semicircular papillte. 



Actinal interradial areas small and triangular, without spinelets, and covered 

 by a thin skin through which the plates are not discernible until specimen is partiallj' 

 or wholly dried. The plates are thin subcircular or elliptical, and not regularlj' 

 arranged. In small specimens they are distinctly spaced. They extend as far 

 as the edge of the fifth inferomarginal. Beyond this ])oint there is a smgle row of 

 what appear to be isolated intermediate plates, extending to tip of ray. These are 

 the lower ends of the ambulacral ossicles, are triangular, the apex being adjacent 

 to a suture between two adambulacral plates. At the tip of ray they are fairly 



