1879.] NATURAL SCIENCES OF PHILADELPHIA. 359 



Encrinidoe. All this tends to explain the extraordinary modifica- 

 tion of characters that took place within the limits of genera at 

 the close of the Carboniferous Era. 



Generic Diagnosis. Calyx large, saucer or bowl-shaped to sub- 

 globose. Plates heavy, convex to tumid, sometimes ornamented, 

 their arrangement unsymmetrical ; sutures strongly defined. 



Underbasals five, of equal size; generally small and forming a 

 eoncavity; in European species comparatively larger and slightly 

 convex. Basals large, fully as high as wide, bent upwards so that 

 the lower half of the plates stands almost at right angles to the 

 vertical axis, and forms a part of the basal plane, oris involved in 

 the concavity. Three of the basals are equal, pentagonal in out- 

 line; the other two modified to accommodate the anal pieces. 

 Radial s scarcely as large as the basals, much wider than high, all 

 pentagonal, the right posterior plate being, however, generally 

 smaller and of a more irregular form. The upper articulating 

 margin of the plate forms a straight line, perfectly filled by the 

 brachials. Brachials one bj r five, always large, at least twice as 

 wide as high, and frequently extended into a large spine, project- 

 ing laterally. Their outer form is almost quadrangular, although 

 they are usually bifurcating plates. They abut laterally, closing 

 the interradial spaces (except at the anal side) by which they 

 appear as if a part of the cal}'x. 



There are generally two arms to each ray or ten to the in- 

 dividual; sometimes only five, as in E upachycrinus simplex 

 Trautschold. They are strong, scarcely diminishing in size to 

 the extremities, and rounded on the outside. They are variously 

 constructed, either of a single or double series of plates, the 

 former being either short, transverse with straight lines, or cunei- 

 form, becoming by degrees alternately arranged and interlocking. 

 Ainbulacral groove wide and deep; Pinnules short and heavy. 



Anal plates generally three, rarely one; succeeding plates form- 

 ing part of the small ventral tube. The lower anal plate is 

 largest, and sometimes attains, for a plate of this kind, unusual 

 dimensions; it is quadrangular in outline, and rests obliquely 

 between the posterior basal and right radial. The second plate, 

 which is next in size and also large, is placed between the first 

 anal and left radial, and above the basal. The third anal is much 

 swollen, and only the lower half of it is included in the calyx. 

 All succeeding plates, which are alternately arranged, decrease in 



