OPHIUROIDEA 185 



Ophioplinthaca, Verrill. 



Tentacle scale, beyond the first pair, cleft or strongly thorny. Radial 

 shields scarcely sunk . . . . O. carduus (Lyman) 



Tentacle scale simple, smooth ; rachal shields usually deeply sunk 



O. chelys (L\-man) 



Ophiomyces Lyman. 



Mouth papillge in two fairly regular series along each side of jaw : 

 ventral plates of arms narrow, longer than broad ; usually two 

 tentacle scales {Illustr. Catalogue Mus. Comp. Zool. vi. 1871, 

 PI. V. 11-13) 0.frutectosusl.yui. 



Mouth papillae more irregularly arranged : ventral plates of arms 

 distinctly broader than long ; usually thi-ee tentacle scales. 

 {"Challenger''' Oph., PI. XIX. 13-15) . O. grandis Lym. 



Ophiolehes L\-man. 



Disk with coarse granules, also on the prominent radial ridges. 



Five arm spines. [Bull. Inst. Oceanogr. Xo. 396, Fig. 1) 



0. bacata Koehler 

 Disk with granules, but radial ridges nearly naked. Six to seven arm 



spines (" Caudan ", PI. III. 31) . .0. retecta (Koehler) 



1. Ophiomitrella Verrill. 



Disk set with short, thick stumps or glassy granules, which 

 do not conceal the scales. Radial shields large and distinct, 

 naked. Tentacle pores small and inconspicuous ; one simple 

 tentacle scale. Mouth papillae simple, papiUiform. 



One species is kno^vn from the British seas, but another, 

 Opliiomitrella gJobuJifera (Koehler), hitherto found only in the 

 Bay of Biscay, 1700 m. ('' Caudan "), and between the Canaries 

 and Cape Verde, 930-1475 m. (■' Talisman "), is very hkely to occur 

 also in the British region of the Atlantic deep sea. 



Key to the species of Ophiomitrella known from or likely 

 to occur in the British seas. 



Disk set with short, thick stumps ; radial shields contiguous ; 

 scales of disk overlapping ; ventral plates of arms widelv 

 si )arated . . . . . 1. 0. clavigera (Ljmigm.) 



Disk ' ith glassy granules : radial shields separated by a wedo-e of 

 scales ; the scales of disk separated by furrows ; ventral plates 

 of arms contiguous . . . O. globulifera (Koeliler) 



