56 



BULLETIN TS, UNITED STATES NATIONAL MUSEUM. 



broadly in contact, but soon becoming longer than wide; outer 

 margin decidedly convex; at tip of arm the plates are triangular 

 and separated from each other. Interbrachial space below closely 

 scaled. Oral shield somewhat pentagonal, with a wide proximal 

 angle, much longer than wide. Adoral and oral plates moderate 

 and subequal. Oral papillae fire or six on a side subequal. Teeth 

 long, narrow, and pointed. Genital slits conspicuous, but genital 

 scales very narrow and almost completely hidden. Each scale 

 carries a marginal series of minute, sharp papillae, which become 

 larger as they approach the upper side of the arm, to form the arm 

 comb; as seen from above this comb is continuous across the base 

 of the arm, and some of the papillae may be borne by either the 



radial shields or the 

 marginal disk scale be- 

 tween them; the pa- 

 pillae are always short, 

 but may be either sharp 

 or blunt. A slight sec- 

 ondary comb may be 

 developed on the basal 

 upper arm plates but 

 it is almost wholly hid- 

 den by the true comb. 

 First under arm plate 

 wider than long, nearly 

 quadrangular; succeed- 

 ing plates small, wider 

 than long, at first pen- 

 tagonal, but soon be- 

 coming triangular and 

 then half-moon shaped, 

 with the proximal side 

 straight and the distal 

 strongly convex; all the plates are widely separated from each 

 other, except second and third, which are sometimes in contact. 

 Side arm plates rather large and low, meeting beneath ev6n within 

 disk but not above until near tip of arm; each one carries four long, 

 slender, acute spines, of which uppermost is decidedly longest, equal- 

 ing one-and-a-half to two joints. Tentacle pores large; oral pair 

 opening into mouth slit and guarded by four to six long, flat, con- 

 spicuous scales on each side; these scales are noticeable for their 

 length, which is much greater than that of the oral papillae. Basal 

 arm pores guarded by several long, sharp scales, of which there are 

 three or four on each side; farther out there are three, two, and 

 finally only one, borne on proximal side; they are all slender and 



Fig. 13.— Ophiura quadeispina. X5.5. a, from above; b, from 

 below; c, side view of two arm joints near disk. 



