58 ECHINODERMA OF THE InDIAN MuSEUM, PART VII. 



c^ ten arms. 



DECAMETRA, p. 15S. 



a - P„ present on all the arms. 



b' ten arms ; size small ; distal cirrus segments nearly or quite as long as broad , 

 cirrus segments with a stronsi serrate transverse ridge (rarely two) ; usually 

 several of the proximal pinnules have segments with strongly produced and 

 spinous distal ends. 



OLIGOMETRA, p. 168. 



b* more than ten arms ; size medium or large ; cirrus segments subequal, short, 

 bearing dorsally paired spines or tubercles ; segments of the greatly enlarged 

 Pj with produced and spinous distal ends ; P^ much larger and stiller than 

 Pi or P3, recurved and horn-like. 



CENOMETRA, p. 153. 



15. — Fajiily Tropiometrid^. 

 The family Tropiometrid;e includes only the single genus Tropiometra. 



16. — Key to the Genera of Calometridae. 

 a' IIBr series 4 (3+4). oreometra, p. 179. 



a* 11 Br series 2, or with ten arms f)nly. 



b' all the lower pinnules slender, comparatively short, subequal in length ; 10-15 

 arms. 



calometra, p. 177. 



b^ P, or P.J considerably longer than, usually from half again to twice as long 



as, the earlier genital pinnules, more or less enlarged and stiffened; more 



than 15 arms. 



c' rays and division series in apposition laterally through more or less 



irregularly developed lateral processes ; the lower part of the animal is 



compact, the sides making a comparatively small angle with the dorso- 



ventral axis. 



pectinometra, p. ls5. 



c^ rays and division series (at least beyond the IBr,) very widely separated, 

 with smooth lateral margins ; the rays and division series make a very 

 large angle with the dorsoventral axis, sometimes being practically at right 

 angles to it. 



d' the anterior interradial processes of the radials separate widely the 

 bases of the [Br,; the lower pinnules are comparatively stout ; arms 



short, witli less than 1 00 brachials. 



neometra, p. 181. 



d^ the anterior interradial processes of the radials are narrow and short, 

 so that the I Br, are in apposition beyond them ; the lower pinnules are 

 very slender; arms long, with more than 120 brachials. 



gephyrometra, p. 184. 



