MONOGRAPH OF THE EXISTING CRINOIDS. ' 253 



larly concave, forming broad lenticular gaps between adjacent plates. The distal 

 outer angles are produced into long narrow horns, which curve toward the am- 

 bulacral groove and slightly outward, and which, though very narrow in lateral 

 view, extend inward for some distance across the pinnule. The proximal outer 

 angles are produced into a broad process rounded at the end, which makes an angle 

 of about 45° with the pinnular and is bent inward under the distal horn-like process 

 of the preceding plate. In the middle of the distal border, at the base of the 

 proximal broad process, is an angular projection, forming approximately a right 

 angle. The side plates are extremely delicate, though everywhere with definite 

 edges. They bear no ridges on the inner side, and have no basal extension over 

 the inner surface of the pinnulars. 



The moderately large, almost circular, covering plates are articulated to the 

 distal side of the proximal process. 



Toward the base of the pinnules the side plates become lower and lower, finally 

 becoming reduced to very narrow horizontal plates and later disappearing alto- 

 gether; at the same time the covering plates become reduced, though much more 

 gradually, finally occurring only as irregular calcareous films in the marginal 

 lappets. 



There are no calcareous deposits in the tentacles. 



An intermediate stage in the reduction of the side plates shows them reduced 

 to somewhat irregular broad crescents with blunted ends, curving proximally, with 

 the circular covering plates just beyond the outer edge of the outer horn, alternating 

 with straight rods of the same height leaning slightly distally, which represent the 

 distal horn-like process and the distal edge. 



The sacculi are situated between the side plates. 



Cosmiometra delicata. — The side and covering plates essentially resemble those 

 of C. crassicirra, but the texture of the side plates appears to be much finer. The 

 proximal outer angle of the side plates is not so much produced as in C. crassicirra, 

 and is not more conspicuous than the median outer angle ; the chord of the reentrant 

 arc between these two is almost parallel to the base, and in this concavity the cover- 

 ing plate rests. As in C. crassicirra^ the notch between the narrow distal process and 

 the median angle gradually deepens imtil the distal portion separates off in the 

 form, in lateral view, of a rod. leaving the proximal portion in the form of a broad 

 crescent with the covering plate on the inner (concave) side of its proximal end. 



Stylometra spinifera. — The side and covering plates are of the same general 

 type as those of Cosmiometra. The side plates are just in contact basally, higher 

 than broad, with slightly concave sides, which leave between them long lenticular 

 gaps for the reception of the sacculi, which outwardly narrow gradually but basally 

 are abruptly rounded off against the appressed bases of two adjacent plates. The 

 outer edge shows a proximal outer angle and an obtuse median angle with an 

 obtusely angular incision between them. The distal angle is produced into a thin, 

 horn-like process, which, however, is broad transversely, curving distally and 

 upward, the angular notch between this and the median angle being much deeper 

 than that between the median and the proximal angles; whereas the base of the 



