1886.] NATURAL SCIENCES OF PHILADELPHIA. 195 



plate is placed on a level with the arm joints, has a like width 

 and, therefore, is easily mistaken for an arm plate. 



The anal plate supports a very stout appendage, composed of a 

 single row of exceedingly large and heavy plates, longitudinally 

 arranged, which, instead of forming into a tube as in the case of 

 other Fistulata, are transversely curved like arm joints, leaving 

 a rather shallow, semicircular furrow on the inner side. These 

 plates are along their back extremely heav}'', as thick as the radials 

 at their upper margins, but they thin out toward their ends, 

 and approaching the furrow become extremely delicate. The 

 proportions of the plates are well shown by our figure of Gatillo- 

 crinus Wachsmuthi (PL 5, fig. 16), in which five of these plates 

 occupy an .inch, while in the same space there are seventeen arm 

 joints. It must be further mentioned that up to that point the 

 plates suffered no diminution in height nor in width, nor is there 

 any decrease in the thickness of the wall, which in Catillocrinus 

 Wachsmuthi, at the top of the fifth joint, is nearly two thirds of 

 the whole width of the appendage. The cross section is semilunu- 

 lar except at the base. The stoutness of the plates on the one 

 side, and the grooved structure on the other, are perhaps due to 

 the great thickness of the radial plates upon which the tube rests; 

 it had to be so necessarily in order to effect a communication with 

 the inner cavity of the calyx. The groove was probably covered 

 during life by perisomic plates. No traces either of a vault or a 

 disk have been observed. 



The arms rise directly from the truncated summits of the 

 radials, without the intervention of axillary plates. There is an 

 arm to every groove, and, hence, some of the radials, contrary to 

 the rule in other Crinoids, support a large number of arms from 

 the same level. The arms are simple, slender, comparatively 

 long, scarcely rounded outwardly, of almost uniform size, and 

 when closed they appear as if united into a solid wall. The arm 

 joints are quadrangular, much longer and somewhat deeper than 

 wide, with parallel sutures. Arm furrows deep, triangular. 



The column is circular, composed of thin joints, the upper part 

 is very stout but tapers rapidly downward. 



Geological Position, etc. The genus is apparently restricted to 

 the Upper Burlington and Keokuk divisions of the Subcarbonif- 

 erous of Aimerica. 



