CLARK: BRITTLE-STARS. 



279 



Amphiura which have more or less naked skin on the disk. It is 

 because of the existence of this group of Amphiuras that Matsumoto 

 has abandoned Ophionephthys, and if the naked disk of this genus 

 were its only character, it would indeed be of little value. But the 

 species, which may be assigned to Ophionephthys, agree in a number 

 of characters and make a natural and fairly homogeneous group. 

 Curiously enough the original and hence, of course, type-species is not 

 typical but in at least two characters differs from the others. More- 

 over it is a West Indian species, whjle all the others are East Indian 

 (from Japan to Australia). It might indeed be desirable to leave 

 Ophionephthys, a monotypic West Indian genus and give the Japanese 

 and Australian species a new generic designation were it not that the 

 Philippine species is very evidently intermediate and could be almost 

 as well assigned to the West Indian as to the Japanese group. Never- 

 theless the differences in the oral armature between 0. limicola and 

 the other members of the genus are serious and if adequate material 

 proves them to be constant, they might well be considered generic. 

 So few specimens of Ophionephthys have as yet been collected how- 

 ever, that it seems best for the present to retain the name for all those 

 amphiurans which agree in the following characters : — Disk (at least 

 in adults) covered with a naked skin, calcareous scales occurring only 

 around the radial shields and rarely near the disk-margin interradially; 

 upper arm-plates small, thin, never very wide nor broadly in contact ; 

 arm-spines numerous, 5-10 on basal joints; oral papillae as in Am- 

 phiura, a pair of block-like thick papillae at tip of jaw and one con- 

 spicuous papilla on each oral or adoral plate (but in 0. limicola there 

 are usually 2 and sometimes 3 small papillae instead, situated on 

 each oral plate); the papilla guarding the first oral tentacle-pore is 

 usually evident and may be very conspicuous; no tentacle-scale (or 

 a single very small one on most pores, in 0. limicola) on the very large 

 tentacle-pores. 



In addition to the species hitherto assigned to Ophionephthys, I 

 refer two species of Amphiura from Japan, described by Matsumoto. 

 I have no doubt that author would himself have called his species 

 Ophionephthys had he regarded the genus as entitled to recognition. 

 One of the species hitherto described as Ophionephthys was based 

 upon several diskless specimens from Brazil. Bell, believing that the 

 loss of the disk indicated a small amount of calcareous matter therein, 

 called his new species Ophioncpht}uis{'t) scsquipedalis. But, aside 

 from the fact that the nakedness of the disk is a pure assumption, 

 his specimens were clearly not Ophionephthys as here defined for 



