OPHIUROIDEA OF THE BAHAMA EXPEDITION. 63 



er; the third and fourth are nearly as wide as long, five-sided, 

 with corners rounded. The first is a short, transverse plate, 

 bearing a row of minute spinules, and separated from the 

 radial shields by one or more supplementary plates. 



Diameter of the disk of the largest, 14 mm.; the arms are 

 broken at the ends. 



Station 2, off Havana, no fathoms, two examples. 



In one specimen, probably owing to repair after injury, 

 two of the radial shields are replaced by a mosaic of small, ir- 

 regular scales, bearing spinules, and the basal dorsal arm- 

 plates, also, are each replaced by several small pieces. 



This species is closely allied to O. hystrix Lyman, from 

 the same region. The latter, as figured by Lyman,* has 

 shorter and more irregular radial shields, separated for about 

 half their length by a wedge of scales; the disk-plates larger 

 and few, bearing much smaller, short, conical, thorny and 

 sharp grains. The basal upper arm-plates are longer and 

 more angular, trapezoidal, and more extensively in contact. 

 The basal under arm-plates are shorter and less triangular; 

 the under arm-plates have a less distinct central lobe; the 

 eight arm-spines are shorter and more unequal. The mouth- 

 papillae, tentacle-scales, and oral shields are, however, very 

 similar in the two forms. 



O . fasciculata Lyman, also from the West Indies, is an- 

 other similar species. It has smaller and very slender disk- 

 spines, shorter and smaller radial shields, closely joined, and 

 without the intervening row of spinules. The dorsal arm- 

 plates are narrower and more widely separated; the six arm- 

 spines are much shorter; the oral shield is broader and less 

 lobed;the tentacle-scales fewer. The mouth-papillae and un- 

 der arm-plates are very similar. 



*Three large specimens of this species are in the Yale Museum, sent 

 by Mr. Lyman. Two of them agree well with Mr. Lyman's type, but 

 the third is much like our type of O. austera. Mr. Lyman probably in- 

 tended to include both forms under his species. But our species is 

 really more nearly allied to O. fasciculata L. 



