A. H. CLARK : TB.V. CRTNOIDS OF THE INDIAN OCEAN. 61 



b* all the pinnules are present. 



c' P.J bears a genital gland and, with the following , is as long as or even 

 much longer than, the first : the cirri are short with few segments. 



BATIIYMETRIN.^, p. 244. 



c* P.J does not bear a genital gland. 



d' cirri long, compressed, deciduous, the distal segments slightly or not at 

 all shorter than the proximal : there are no dorsal spines ; o])posing spine 

 absent, more rarely feebly developed ; P, is composed of numerous 

 squarish or rounded segments, or much reduced. 



THYSANOMETRIN.E , p. 242. 



d" cirri few, short, with few segments, which are shorter distally than 

 proximally, irregularly disposed on a low hemispherical centrodorsal ; an 

 opposing spine is present on the penultimate, but there are no dorsal 

 spines. 



ANTEDONIN^, p. 227. 



d* cirri numerous, long, composed of numerous segments which are much 

 shorter distally than proximally, with the distal segments spinous or 

 strongly carinate, and evenly distributed over and closely crowded on a 

 large hemispherical or rounded conical centrodorsal 



HELIOMETRIN.^, p. 238. 



20. — Key to the Genera of Antedonid.^. 



a' P^ absent. 



b' cirri in ten well-separated columns on a long conical centrodorsal ; P, also 

 absent. 



BALANOMETRA, p. 238. 



b* cirri closely crowded on a rounded conical or hemispherical centrodorsal : 

 Pj present. 



c' interradial areas with two or more columns of perisomic plates ; I Br series 

 and lower brachials rounded and free laterally ; synarthrial tubercles not 

 developed ; size very small. 



ERYTHROMETRA, p. 233. 



c* disk naked ; TBr series and lower brachials in close apposition and strongly 

 flattened laterally ; synarthrial tubercles very prominent : size medium. 



PEROMETRA, p. 232. 



a^ P„ present. 



b' P.2 bears a genital gland ; size usually very small. 

 c' P| as long as, or slightly longer than, P^. 



THAUMATOMETRA , p. 245. 



c* Pj shorter than P.^^. 



BATHYMETRA, p. 244. 



