A. H. CLARK : THE CRINOIDS OF THE INDIAN OCEAN. 51 



g' cirri comparatively slender, with more than 25 segments, of 

 which the distal are short and bear dorsal spines ; Pj usually much 

 enlarged with stout segments, sometimes like P, but slightly 

 shorter ; genital pinnules not expanded. 



(0) THALASSOMETRID^, p. 188. 



{Cf. key 17.) 



g* cirri stout, with usually less than 25 segments which are subequal 

 and do not develop dorsal spines distally ; P, and P.^ longer an d 

 mere slender than the following, comijosed of very numerous 

 short segments ; genital pinnules expanded. 



(0) CHARITOMBTBID^, p. 215. 



(Cf. key 18.) 



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, 

 f cirrus segments subequal, almost never longer than broad, bearing 



paired spines dorsally ; lower pinnules with spinous processes on the 



distal ends of the segments. 



(0) COLOBOMETRID^, p. 153. 



(Cf. key 14). 



f^ some at least of the cirrus segments as long as or longer than broad ; 



cirri smooth, carinate dorsally, or bearing single median dorsal 



spines. 



g' Pi slender and delicate, usually flagellate, with much elongated 

 segments; cirri delicate, deciduous, with expanded articulations 

 in the proximal half ; never more than twelve arms. 



(M) ANTEDONID^, p. 227. 



(Cf. keys 19, 20.) 



g*^ P, if slender and delicate, composed of shorter and more 

 numerous segments than its successors, which are considerably 

 enlarged ; P, may be much longer than its successors with very 

 numerous short segments, or it may resemble its successors in 

 being stiff and spine-like; always at least twenty, usually over 

 thirty, arms. 



h' one or more of the proximal pinnules enlarged, stiffened, and 

 spine-like, usually with less than 18 long segments; division 

 series well separated, the component ossicles with prominent 

 ventrolateral processes. 



(O) STEPHANOMETEID.E, p. 131. 



(Cf. key 11.) 



