44 ECHINODERMA OF THE INDIAN MuSEUM, PART VII. 



a* cavity in the centrodorsal containing the chambered organ and overlying struc- 

 tures very large ; only the interradial processes of the rosette (when present) 

 form "spout-like" processes; rosette nearly or quite on a level with the dorsal 

 surface of the radials ; pinnules all cylindrical or more or less flattened , and 

 slender, all (rarely excepting Pj) composed of much elongated segments ; the 

 post-radial series divide but once, or not at all. 



COMATULIDA Macrophreata, p. 227. 

 {Cj. keys 2—5; 19—22.) 



2. — Key to the Comatulid Families. 

 a^ the arms do not divide, but are composed of a linear series of ossicles, of 

 which the radial is the first. 



b' five short arms; a pseudo-syzygy between the first two post-radial ossicles, 

 and a syzygy between the fifth and sixth; proximal pinnules stout and 

 triangular in cross section; disk small and compact, never black. 



(0) ZYGOMETRIDiB, p. 9i>. 



(C7/. keys 3—5; 9.) 



b^ five or ten very long and very slender arms ; the first syzygy is between the 

 fourth and fifth post-radial ossicles ; proximal pinnules long and very 

 slender, cylindrical or slightly flattened ; disk black, the perisome extending 

 far up on the arms. 



(M) PENTAMETROCRINlD.i;, p. 247. 



(67. keys 3, 4, 21.) 



a^ the arms always divide at the second post-radial ossicle, and may divide 



still further. 



b' a circlet of basals separates the centrodorsal from the radials ; centrodorsal 



Ion'', conical, the cirrus sockets in 10 or 15 columns, well separated, each 



with a raised horse-shoe-shaped rim proximally and laterally ; no pinnules 



on the first 10 or 12 brachials. 



(\I) ATELECRINIDJE, p. 251. 



{Cj. keys 4, 22.) 



b* no basals • cirrus sockets without a raised rim ; ))innules from the second, or 

 at furthest the fourth, brachial, onward. 

 c^ oral pinnules long and slender, composed of very numerous short segments 

 and bearing a comb distally ; mouth usually marginal to subcentral ; 

 anal tube usually central. 



(0) COMASTERID^, p. 68. 



(Cj. keys 4, 5, 7, 8.) 



c* oral pinnules smooth distally, without a comb ; mouth always quite, or 

 very nearly, central; anal tube lateral. 



