186 



BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



curved, deeply sunken below the disk scales, widely separated 

 throughout. Upper arm plates wider than loh^^, with a convex or 

 straight distal margin and a strongly convex, often angular, proximal 

 margin ; thus somewhat broadly pentagonal with only the two distal, 

 lateral angles marked; they are much swollen and widely separated. 

 Interbrachial spaces below rather broad, somewhat heart-shaped, cov- 

 ered by irregular plates wliich are large at the margin but become 

 very small near the oral shield. Genital slits short but rather con- 

 spicuous. Oral shields rhombic or pentagonal, about as wide as long. 



Adoral plates long 

 and narrow, about 

 as wide without as 

 within, where they 

 meet; oral plates very 

 small. Oral papillae 

 about five on a side 

 and one at apex of 

 jaw, the outer ones 

 are truncate, but the 

 inner are more or less 

 sharply pointed; be- 

 tween the penulti- 

 mate and antepenulti- 

 mate papilla? are sev- 

 eral small granules, 

 which apparently 

 serve as tentacle scales 

 to the oral tentacle 

 pore. First under 

 arm plate pentagonal, 

 about as wide as long; 

 _, secontl plate nearly 



-v.^^-^^ ^ triangular, but trun- 



FiG. 85.— ophiomitra bythiaspis. X 5. a, from above; b, from catcd at the angles, 

 below; c, side view of two arm joints near disk. wider than lono" " Suc- 



ceeding plates nearly tetragonal, much wider than long, widely sep- 

 arated from each other. Side arm plates very large, meeting both 

 above and below; each plate carries, on rather a conspicuous vertical 

 ridge, six or five long slender arm spines, of which the uppermost, 

 which may equal two joints, is the longest (sometimes the second is 

 the longest), smoothest, and sharpest, while some of the lower, 

 shorter spines are quite rough near the tip. Tentacle scale single; 

 those on the basal pores are very large and broadly oval and are 

 often accompanied by a second, smaller scale; bej^ond the third 

 pair of pores the scales are narrower and are pointed. Color (dried 

 from alcohol), very light gray. 



