A. H. CLARK : THE CRINOIDS OF THE INDIAN OCEAN. 53 



enlarged with stout segments, sometimes like P.^ but slightly 

 smaller ; genital ])innules not expanded. 



(O) THALASSOMETRID^E, p. 188. 



(67. key 17.) 



g'' cirri stout, witli usually less tlian 25 segments which are subequal 

 and tlo not develop dorsal spines distally; P, and P^ longer and 

 more slender than the following pinnules and composed of very 

 numerous short segments ; genital pinnules expanded. 



(O) CHARITOMETRID^, p. 215. 



(Cf. key 18.) 



e^ middle and distal pinnules slender, cylindrical, composed of elongated 

 segments which, in the distal, have swollen articulations ; side and 

 covering plates entirely absent, or very feebly developed. 



(0) HIMEROMETRIDiE, p. 107. 



(Cf. key 10.) 



6. — Key to the Families of the Stalked Crinoids. 



a' Stem entirely composed of very short more or less pentagonal columnars with 

 petaloid markings upon their apposed faces, and including regularly spaced 

 nodals bearing whorls of cirri ; distal end of stem always discarded in the adult. 



PENTACRINITID.E, p. 252. 



(Of. key 23.) 



a* stem always terminating distally in a terminal stem plate or root ; nodals and 

 cirri entirely absent, or confined to the proximal portion of the stem and rudi- 

 mentary. 



b' proximal columnars pentagonal or stellate, sometimes including nodals 

 bearing rudimentary cirri, but the greater part of the stem composed of 

 short columnars which are circular in outline, and without nodals. 



apiocrinid.^, ]). 271. 

 (Cf. key 24.) 



b* all the columnars with circular or elliptical ends, never pentagonal or stel- 

 late; no trace of nodes or cirri. 



c^ columnars cylindrical, their articular faces marked with radial crenelle ; 

 arm bases occupying only a part of the distal border of the radials ; usu- 

 ally three basals. 



HYOCKINID.E, p. 272. 

 {Cf. key 25.) 



c* columnars with elliptical ends, the axes of succeeding ellipses making 

 nearly or quite a right angle with each other, the articular faces marked 



