'20i PROCEEDINGS OF THE ACADE>rY OF [1881. 



times with little nodules, in some species with all the plates 

 strongly nodose or almost spiniferous ; symmetry slightly bi- 

 lateral. 



Basals four, three of them equal and pentagonal, the fourth 

 larger and hexagonal, the latter directed to the left antero-lateral 

 ray, not posteriorly. 



Radials 3X5; the five first hexagonal and joining laterally; 

 the plates of the second seiies hexagonal, the first interradial and 

 anal plate interposed between them ; the third pentagonal and 

 bifurcating. They support on their upper sloping sides two to 

 three secondary radials (2-3 X 10), with one or more — though 

 sometimes none — in the axil. The secondary radials are suc- 

 ceeded in a direct line bj' two rows of plates, which sometimes 

 interlock, but which more frequently are placed side by side. 

 The plates which represent higher orders of radials, are separated 

 by a deep vertical suture, and formed into a long brachial appen- 

 dage or free ray, which terminates in an arm. 



The free rays give off laterally, throughout their length at 

 certain intervals, from each third or fourth joint, or less often, 

 and from opposite plates (not alternately), small armlets, com- 

 posed of two rows of interlocking plates, with short pinnules on 

 alternate sides. The plates which compose the appendages are 

 wider than high, their upper and lower sides parallel, except the 

 arm-bearing pieces which are depressed pentagonal. The length 

 of the armlets difiers according to their position ; aU extend to 

 the same general height, and hence those nearer the body are 

 longer, the length decreasing proportionately upward. 



In young specimens, all arms are given oflf from the free raj^s ; 

 while in the adult, the lower portion of the proximal arm is 

 often enclosed within the calyx, and sometimes even separated from 

 the main trunk by small plates. 



There is onl}- one brachial appendage to each ray, and this, as 

 stated before, is composed of two rows of plates which rest upon 

 a bifurcating plate. This construction leaves no doubt that the 

 two rows, which are separated hya deep longitudinal suture, often 

 by interaxillary pjlates and small intermediate pieces scattered 

 between them, represent two distinct brachial appendages, wliich 

 became anchylosed throughout their length, contrary to Maria- 

 crinus, in which under similar conditions, the equivalent parts 

 remained detached. 



