506 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



bulacral spines tapering and pointed, then compressed, broad and 

 often bifid at tip, the 2 parts being truncate. These spines are about 

 2-2.5 adambulacral plates in length, and increase very slightly up to 

 the fifteenth, whence they soon lose the truncate tip and decrease 

 gradually in length. At the end of the costal region the subambulac- 

 ral spine is about three-fourths the length of the adjacent lateral spine. 

 On the aboral apophysis of the plate is a single furrow spinelet about 

 the length of the plate. Beyond the proximal two-thirds of the 

 costal region this is usually lacking. 



Mouth plates with an expanded, curved, actinostomial border, a 

 very excavated furrow margin and a less expanded margin adjacent 

 to first adambulacral. No suboral spine. At the outer furrow corner 

 is 1 furrow spinelet about one-third the sutural length of plate. Acti- 

 nostomial margin with 4 or 5 spinelets (8 to 10 for the combined 

 plates) spread fan- wise toward actinostome and mouth of furrow, 

 where they interdigitate but do not fuse. The lateral spinelets are 

 slightly the longest as a rule. They bear a few pedicellariae. 



Gonads are 2 to each ray. 



Madrepodic body small and turned toward the margin. 



Type.—C2ii. No. 37019, U.S.N.M. 



Tyye-locality. — Station 5217, between Burias and Luzon, 105 

 fathoms, coarse gray sand ; 1 specimen. 



Distribution. — Known only from the type-locality. 



Remarks. — In general appearance this species resembles Odinia 

 austini Koehler and is about the same size as that form, from which 

 it differs in having a more extensive costal region, the first costa 

 being opposite the fifth instead of the fifteenth adambulacral plate; 

 in having on the proximal adambulacral plates an aboral furrow 

 spinelet, and, judging by Koehler's figure (1909, pi. 13, fig. 6), a 

 differently formed oral angle. In 0. penichra the mouth plates are 

 much larger than in austini^ the actinostomial margin is broader, the 

 pair of plates are more constricted medially, the spinelets bear pedi- 

 cellariae, and there is a distal furrow spinelet. According to Koeh- 

 ler's figure the rays are joined together as far as the beginning of the 

 sixth adambulacral plates; in O. 'penichra only the first three are 

 joined. The mouth plates also differ from those of 0. dlarhi Koeh- 

 ler (1909, pi. 4, fig. 7) both in form and in lacking a suboral spine. 

 In O. fenichra the plates are much expanded at the outer as well 

 as the inner end, and there is an aboral furrow spinelet. In neither 

 clarki or austini is this the case. O. clarki differs further in having 

 more numerous costae, more conspicuous costal spines, a greater dis- 

 tance between the disk and the first costal spine, and 1 suboral spine. 

 In O. pacifica Fisher, from the Hawaiian Islands, the disk spinelets 

 are cylindrical or swollen at the tip, which ends in many minute 

 points, and there are more often 2 or 3 spinelets to a plate than 1; 



