232 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



pieces 10, subrhomboidal in outline, arranged in pairs, each pair 

 being formed of two of the marginal series of ray plates; on the lower 

 inner edge there are five spines, and extending from each pair, 

 over the mouth, is a bundle of rather long ones. 



"Rays apparently very flexible, contracted toward the mouth; 

 six series of plates are exposed on the ventral side of each ray. The 

 two middle series [ambulacrals] alternate regularly, and interlock 

 along the mesial line; they are about twice as long in the direction 

 of the ray, than measuring transversely; each piece is contracted 

 in the middle on the inner side to admit the wide ends of the two 

 pieces immediately opposite, and on the outer side to form a pore- 

 like impression, between them and the outer series of plates; four 

 [five or possibly six] of these plates in each range of each ray are 

 included within the disk, and the series terminate abruptly at a 

 distance of one and a half lines from the inner end of the oral plates; 

 from the margin of the disk to the extremity of the ray there are 

 about 16 pieces in each range. The pores mentioned above, are 

 occupied by a series of loosely fitting, obtusely conical or pyramidal 

 plates, some of which distinctly show a deep depression in the top, 

 and may have been perforated. Outer or marginal pieces [side 

 plates] flat, placed on edge, and directed obliquely outward so as 

 to overlap each other; the two free edges, that is, the one toward 

 the point of the rays and the one seen on the ventral surface, are 

 lined \\ith from 10 to 12 short club-shaped spines, varying somewhat 

 in length. The marginal [side plates] and middle [ambulacral] series 

 of plates articulate by means of corresponding prolongations from 

 the sides of the plates. These prolongations arise from near that 

 end of the plate which is directed toward the mouth. 



"Dorsal side of rays composed of two rows of alternating and 

 interlocking plates, which near the disk are very deeply sculptured 

 and about as wide as long, becoming gradually less excavated, and 

 longer in proportion to the width, toward the point of the rays; on 

 each side they articulate with the upper edge of the oblique mar- 

 ginal series of plates [these are the ambidacral plates seen from the 

 dorsal side, either because there were no dorsal plates or because 

 there was an integument]. 



"Breadth of disk, 0.60 inch; breadth of arm at margin of disk, 

 0.16 inch; length of same from oral plates, 0.88 inch. This species 

 is related to Protaster Jiexuosus.'' 



Formation and locality. — "This species has been found at dift'er- 

 ent elevations from near low-water mark in the Ohio River [that 

 is, in basal Eden] to the top of the hills at Cincinnati," in the upper 

 Maysville beds. The type-specimens of P. Jlexuosus were found 

 by Mr. C. B. Dyer and are now in the collection of Harvard Uni- 

 versity (Nos. 17, 18). Those of P. Jimhriata were obtained by 



