A. H. CLAEK : THE CRINOIDS OF THE INDIAN OCEAN. 63 



f" P, shorter than Pj, which is more or less enlarged and stiffened. 



PEROMETEA, p. 232. 



e^ 16 or less cirrus segments. 



f P, shorter than the succeeding pinnules. 



g' Pj hears a genital gland, and is stouter than P,. 



BATHYMETRA, p. 244. 



g'^ P.^ without a genital gland, resembling P[. 



h^ elements of the division series and brachials with very strongly 

 produced and serrate distal ends. 



TOXOMETRA, p. 232. 



h^ elements of the division series smooth ; brachials with the distal 

 ends slightly, if at all, produced. 



IRiDOMETRA, p. 230. 



f'^ Pi much the longest pinnule. 



g' P, about twice as long as P.^ ; segments of the lower pinnules 

 strongly overlapping. 



COMPSOMETRA, p. 229. 



g* P^ about one third longer than P.^, which, in turn, is about one 

 third longer than P.^ ; segments of the lower pinnules smooth. 



MASTIGOMETKA, p. 227. 



21.— Key TO THE Genera of Pentametrocrinid^. 



a' five arms. 



pentametrocrinus, p. 250. 

 a* ten arms. 



decametrocrinus, p. 247. 



22. — Family Atelecrinid^. 

 The family Atelecrinida? includes only the genus Atelecrinus. 



23. — Key to the Genera of Pentacrinitid.e. 



a- 'I'he arms do not divide before the fourth post-radial ossicle ; one or more pin- 

 nules precede the first axillary. 



METACRINtTS, p. 264. 



a^ the arms divide on the second post-radial ossicle ; no pinnules before the first 

 axillary, 

 b^ ten arms; stem slender, smooth, nearly circular in cross-section. 



HYPALOCRINUS, p. 261. 



b* more than ten arms, 

 c' all the division series of two ossicles, united by pseudo-syzygy ; the second 

 brachial of the free undivided arms bears the first pinnule ; the third and 



