270 PROCEEDINGS OF THE ACADEMY OF [18*79. 



that of Forbesiocrinus, except that the upper part of the interra- 

 dial area is less substantial and compact ; but their posterior 

 aspect exhibits in Taxocrinus a small lateral proboscis, while in 

 Forbesiocrinus the space is filled with heavy plates, in the latter 

 an almost pentamerous symmetry, in Taxocrinus (except in the 

 Swedish species), a distinct bilateral one. This we consider the 

 best distinction between the two genera. (Compare Diagram, 

 PL 15, Fig. 2.) 



An examination of a very large series of well-preserved speci- 

 mens of the two genera has led us to this conclusion, and to a 

 modification, to this extent, of the opinion intimated by us here- 

 tofore (Proceed. Phila. Acad. Nat. Sci., 1878, p. 254), that there 

 is no distinction between these genera. We find that in practice 

 we can separate them quite satisfactorily by the characters herein 

 indicated, and, accordingly, we propose the following revised 

 generic diagnosis : 



A. Typical form. 



Body, including arms, rather short, depressed ; calyx cup- or 

 bowl-shaped, with bilateral symmetry. Underbasals three, some- 

 times very small, unequal in size, the two larger ones pentangular, 

 the smaller quadrangular. Basals five, four of them equal and 

 with acute upper angles, the fifth larger, generally with truncated 

 upper sides. Primary radials three rarely four by five, of nearly 

 equal size, wider than high, quadrangular in outline, except the 

 upper one which is pentangular. Secondary radials varying in 

 number from three to six the former most prevalent slightly 

 smaller than the primary radials, and resembling them in general 

 form. Tertiary radials like the preceding, only comparatively 

 smaller and supporting the arms. 



Arms dichotomizing once or twice, composed of single, short 

 joints, more or less rounded on the back ; sutures frequently 

 sinuate, and sometimes provided with supplementary patelloid 

 plates. Interradials none to three or more as many as nine have 

 been observed extending as high as the top of the second or 

 third primary radials, with very minute, irregular plates above, 

 which fill the entire space to the top of the secondary radials, the 

 axillary spaces, sometimes enclosing the first arm plates, and 

 probably covering the entire ventral side of the body. 



Some species have from one to three regular axillary plates, 

 with occasionally a single plate in the axil between the tertiary 



