226 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



somewhat between the adoral plates ; this angle is bounded by slightly 

 excavated sides ; the lateral angles are rounded, and the distal border 

 is slightly convex. The adoral plates are elongated and rather nar- 

 row, a little tapering inwardly, and they, terminate in rounded angles 

 which are not in contact in the median interradial line ; these plates 

 are broadened outwardly, and they send off a very narrow process 

 which separates the mouth shield from the first side arm plate. The 

 oral plates are high and rather broad. The tooth papillae at first 

 form two regular lateral rows, within which the other papillae form 

 sometimes one, and sometimes two, very irregular rows. 



The upper arm plates are lozenge-shaped, longer than broad, with 

 the proximal angle truncated ; the two proximal borders are markedly 

 longer than the two distal borders, and the maximum width of the 

 plate is nearer the distal angle, which is obtuse. All these plates are 

 in contact. 



The first under arm plate is pentagonal, a little longer than broad, 

 with a very obtuse proximal angle bounded by two straight sides ; the 

 lateral borders are convergent and straight, and the distal side is also 

 almost straight. The following plates are very large and elongated r 

 longer than broad, with a straight proximal border, a very broad 

 and convex distal border, and divergent sides excavated by the ten- 

 tacle pores. These plates are separated by a narrow interval occu- 

 pied by soft tissue. 



The rather strongly projecting side arm plates carry at the base 

 of the arms five slender transparent and pointed spines. The first 

 ventral spine is very short and is almost immediately transformed 

 into a hook; beyond the disk the length of the following spines in- 

 creases rapidly from the second, which is shorter than the segment,, 

 to the last, the length of which reaches four segments. These spines 

 are smooth in their proximal portion, and in their distal half are 

 furnished with very strong and sharp well spaced teeth. 



There is a small, rather thin, pointed and spiniform tentacle scale 

 (pi. 97, fig. 6<?), but it appears to be absent on the three first arm 

 segments ; this scale can never be mistaken for the first ventral spine r 

 which is very rapidly converted into a three branched hook (fig. 6a) . 



The general color is pinkish gray. A large brownish-purple spot 

 appears toward the distal angle of the upper arm plates, but there 

 is no continuous median line. The ventral surface is pink; a some- 

 what darker median line interrupted toward the distal border of each 

 ventral plate runs all along the arms. The spines are pink and some- 

 times show slight purple annulations. 



Affinities and distinctive features. — Ophiothrix deceptor is espe- 

 cially close to O. lepida Loriol, O. fallax Loriol, and 0. purpurea 

 Martens. It is immediately distinguished from O. lepida by the 



