376 PROCEEDINGS OF THE ACADEMY OF [1888. 



large, limb-like projections, deeply incurved between the bases of the 

 rays. This form which occurs also at Dudley, associated with C. 

 Tugosus, is usually labeled as such in collections. 



The reticulate arm structure, which distinguishes Crotalocrinus 

 from all other crinoids, is its most interesting character. The arms 

 are deeper (from the dorsal to the ventral side) than they are wide, 

 they extend to a great length, and bifurcate just often enough, and 

 at such intervals in C. rugosus, to fill up the sjDaces necessary to form 

 a complete circle with the arms in lateral contact out to the periph- 

 ery, and the number of branches in the adult specimen, when perfect 

 must have been enormous. In our specimen of C. rugosxis (PI. XIX, 

 fig. 1), at the height of the fifteenth joint, there are fortj- rami to 

 each ray, and this is not more than one third their full length, so 

 that the number of ultimate divisions would amount in this speci- 

 men to at least five or six hundred. The joints at the same height 

 are of the same length, and the sutures are in the same line all 

 around, so that they form regular concentric circles. Each joint has 

 tv/o lateral projections given ofi'from the middle part of each side, 

 which meet with those of adjacent branches, forming points of union 

 by which the arms are connected throughout, but leaving oj^en 

 spaces or meshes which j^roducethe reticulate appearance. The arms 

 of JEnallocrinus resemble those of Crotalocrinus in their mode I'f bi- 

 furcation and extraordinary length, but are not connected laterally 

 except for a few of the lower joints. They have, however, frequent- 

 ly, if not always, lateral projections along the joints on each side, and 

 hence possess the cross-shaped arm joints of Crotalocrinus (PL XIX, 

 fig. 6°''^"). The sutures between the joints are also in the same line, 

 and do not alternate as we formerly supposed. 



The mode of insertion of the higher radials upon the first radial 

 is very peculiar, and has not hitherto been understood. We might 

 have still remained in ignorance about it, had it not been for the 

 fortunate discovery among our Dudley specimens of an isolated first 

 radial with the succeeding radials attached, so that we could see 

 them from all sides (PI. XX, fig. 4). By the aid of this, and a 

 very interesting, much weathered specimen, loaned us by Dr. 

 Lindstrom, we are enabled to describe and illustrate the position of 

 these parts quite satisfactorily. The plates frouL the second radial 

 up are of considerable size, but they are not always visible on the 

 dorsal side. In C. pnlcher they are plain enough (PI. XX, fig. 1), 

 but in C. rugosus they often appear as mere points or thin edges 



