356 PROCEEDINfJS OF THE ACADEMY OF [1890. 



We have recently been fortunate in ])rocuring fi-oni Montgomery 

 Co., Indiana, a large number of specimens, some 50 or 60, compris- 

 ing 7 species of Cyathocrinua in which the entire ventral structure 

 is in excellent preservation, in many of them to the very end of the 

 ventral sac. They were obtained by removing the arms in some of 

 the most perfect specimens, a sacrifice for which we were richly re- 

 warded. We have also procured from iSweden, through the kind- 

 ness of Prof. G. Lindstnim, careful drawings of some of the types in 

 the Stockholm Museum which, together with the specimens above 

 mentioned, throw a flood of new light upon the ventral structure of 

 this difficult group, and lead to the conclusion that the various spe- 

 cies are built on a similar plan, and do not differ so essentially as 

 it appeared to us at first from Angelin's figures. The most aberrant 

 form is probably represented by Cyathocrinns alutaeeus, of which we 

 give an enlarged figure (PL IX, fig. 1). In this species, the greater 

 part of the ventral surface is occupied by 5 large well defined orals 

 which are arranged in the same manner as those of the Camerata; 

 the posterior plate is larger, and its upper end is inserted between 

 the four others. The orals are surrounded by numerous irregular 

 pieces, of which the outer ones abut against the radials. There are 

 no large interradial plates, nor regular rows of side or covering 

 pieces such as we find in Cyathocrinns laevis, but alternating with the 

 orals, and resting against them, there is toward each ray a sub-tri- 

 angular piece, resembling the so-called radial dome plates of Platy- 

 crimis. 



The spcimens, PL IX, figs. 2-3, both of which Angelin referred to 

 Cyathocrlnus laevis are either distinct species, or one of them is in a 

 more advanced stage of growth. That represented by fig. 3 (Iconogr. 

 Crin. Suec, PL 26, fig. 2) probably at one time had orals like C. 

 ahitaceus, but these were partly resorbed and replaced by other 

 plates. In fig. 2 (Iconogr. Crin. Suec, PL 26, fig. 36), the resorption 

 of the orals was apparently complete, and their place is occupied by 

 irregular covering pieces, which join in the center. Farther out the 

 ambulacra have well defined side pieces, and small covering plates 

 close the food grooves. 



A very different structure is seen in the specimen, Revision 

 Palaeocr. Pt. Ill, PL IV, fig. 2, from the Burlington and Keokuk 

 Transition beds ; in which it appears as if there had been 5 large 

 interradial plates, leaving a wide open space in the center. The 

 plates meet laterally, and form upon their edges deep grooves for the 



