50 echinoderma of the indian mttsettm, part vii. 



5 Key to the Families of Comatulids inclttding Species with more than 



TEN Arms. 



a' Ten radials ; each post-radial series divides once, giving twenty arms. 



(M) antedonid^, p. 227. 

 (Cf. keys 19, 20.) 



a'' five radials • one or more of the post-radial series divides at least twice. 

 b> IIBr 2. 



c' oral pinnules long and slender, composed of very numerous short seg- 

 ments and bearing a comb distally ; mouth usually marginal to sub- 

 central ; anal tube usually central, or nearly so. 



(0) COMASTERID^, p. 68. 



(C/. keys 7, 8.) 



c^ oral pinnules smooth distally, without a comb ; mouth always central; 

 anal tube lateral. 



d' elements of the IBr series united by pseudo-syzygy , appearing like a 

 true syzygy externally. 



(O) ZYGOMETRID^, p. 99. 



{Of. key 9.) 



d* elements of the IBr series united by synarthry. 



el all the pinnules sharply triangular or prismatic, rather stout, the 

 outer with comparatively short segments which do not have swollen 

 articulations ; pimiule ambulacra bordered with well-developed side 

 and covering plates. 



fi P| very delicate, flexible, and weak, the first two segments greatly 

 enlarged , the remainder very small and squarish ; P.-, and usually 

 also some of the following pinnules much elongated, enlarged, and 

 stiffened, with elongated segments; elements of the division series 

 thin dorsoventrally and well separated, but sometimes with broad, 

 more or less irregular, ventrolateral processes; disk globose, 

 compact, entirely enclosed by a solid pavement of plates ; muscular 

 fossse on the articular faces of the radials transversely linear. 



(0) calometrid^j:, p. 177. 

 (Cf. key 16.) 



f* P longer than P,^ ; or, if shorter, resembhng it ; P.^ resembling the 

 succeeding pinnules; elements of the division series very deep 

 dorsoventrally and sharply flattened laterally against their neigh- 

 bours without ventrolateral processes; ventral surface of disk 

 usually concave, the sides not visible; surface of disk studded with 

 rounded calcareous plates which very rarely form a compact 

 pavement; muscular fossae on the articular faces of the radials 

 very high, much higher than broad. 



