PROCEEDINGS OF THE NATIONAL MUSEUM. 261 



interradial plates. On such specimens more or less similar two-valved 

 pedicellariai are found on tlie marginal plates and on the abactinal 

 plates of both the rays and disk. The adambulacral spines consist, in 

 the larger specimens, of an inner or furrow-group of five or six rather 

 slender elongated spines, which arise from a curved and jirominent 

 base line and j)roiect inward in a more or less divergent group, in which 

 the middle spines are somewhat longer than the rest; these spines are 

 mostly flattened in a direction transverse to the rays and are subacute 

 at the tip; external to these, on the actinal side of the plate, there is a 

 somewhat curved longitudinal row of about six spines, which are much 

 shorter than the inner ones, their length being less than half, while the 

 three middle ones are also somewhat stouter than the inner or furrow- 

 spines, and considerably larger than those adjacent to them in the same 

 row ; each plate bears also an outer, incurved marginal series of short, 

 blunt spinules, scarcely larger tlian and similar to the granules of the 

 adjacent plate. They form a marginal row around the outer portion of 

 the plate, and often form, with the median series, a more or less circular 

 or elliptical group, external to the furroAv series; but in other speci- 

 mens the two sets appear rather as parallel, longitudinal rows. The 

 furrow ends of the adambulacral plates are broadly curved and j)romi- 

 nent and j)roject somewhat into the furrow, leaving rather deep inden- 

 tations between them, which form rudimentary fascioles. 



The jaws are furnished with numerous rather stout, flattened spines, 

 of nearly equal size; of these, about three projecting inward from the 

 angle of the jaw are a little the longest, and the median one is a little 

 more prominent than the others. Distal to these, on each margin there 

 may be eight to ten somewhat smaller, blunt, transversely compressed 

 spines standing in a single row. The actinal surface of the jaw-plates 

 is slightly convex and but little prominent, the two plates forming 

 together a broad oval, upon which, proximally, there is a pair of short, 

 rather stout, angular spines, which form the apex of an oval group of 

 smaller and shorter spines, formed by two rows on each half of the jaw; 

 the more distal of those of the outer row, and all those of the inner rows, 

 are similar in size and form to the granules of the adjacent interradial 

 plates. 



This species was taken by the U. S. Fish Commission steamer Alba- 

 tross in 1882 at station 1122, oft" Martha's Vineyard, in 351 fathoms, and 

 at five stations, in 1885, between N. lat. 42° 55' 30", W. long. 50^ 51', 

 and N". lat. 39° 47' 07", W. long. 70° 35', in 471 to 721 fathoms. 



Most of the specimens, including all the larger ones, were taken at 

 stations 2429 and 2552, in 471 and 721 fathoms. 



Variations. — The essential characters of this species do not vary 

 largely in specimens much smaller than those described. The smallest 

 specimen seen has the radius of the disk 8 mm. and that of the rays 

 18 mm. This specimen agrees closely with the largest in general appear- 

 ance and most of the details of structure. But the dorsal parapaxillae 



