188 PROCEEDINGS OP THE ACADEMY OP [1886. 



greater part of tlie underbasal disk, whicli became more elongate, 

 until at last the suture lines between the plates disappeared en- 

 tirely, although in the j'oung Crinoid these are well marked. 

 Owing to the very considerable clwinges of form, which occur in 

 the growing animal, it is extremely' difficult to identifj' the species 

 of this genus, and we fear that several of those described repre- 

 sent merely different stages of the same species. 



Agassizocrinus globosus and A. papillatus Worthen have been 

 referred by us to Cromyocrinus ; his A. hemispJiericus, in wliicli 

 the underbasals do not extend beyond the column, is either 

 Eupachycrinus or Scytalocrinus, probabl3^ the latter. 



Generic Diagnosis. Form of calyx elongate, composed of mas- 

 sive plates, and containing a comparatively small visceral cavity. 



TJnderbasals extremely large ; obconical ; almost solid ; witli a 

 very small inner cavity. Young specimens have an articuLir scar 

 for the attachment of a column, pierced by an axial canal ; this, 

 however, becomes obliterated soon after the Crinoid enters free 

 life. The inner cavity lodges the chambered organ, and is pro- 

 vided with six deep pits, a central one surrounded by five others, 

 which either constitute the chambers of this organ or their lower 

 extensions. 



Basals large, three of them hexagonal, two heptagonal, but they 

 appear to be pentagonal and hexagonal, owing to the convex form 

 of the two lower sides. The heptagonal plates enclose, and partly 

 support, the azygous pieces, consisting of the azygous plate proper, 

 which has a sloping position and is generally large, a smaller anal 

 plate, and the first plate of the ventral tube. The size and form 

 of the tube is not known, but it was evidently small, perhaps 

 similar to that of Gromyocrinus, with which Agassizocrinus agrees 

 in the arrangement of its azygous plates. 



Radials unusually small ; wider than high ; the upper face trun- 

 cate ; they are all pentagonal, four of them of nearly equal size, 

 the fifth one considerably smaller and of irregular form. The 

 articular facets are on a level with the outer edges of the plates, 

 they are somewhat extended inward, and pierced by a transverse 

 axial canal. The articulation between calyx and arms is regu- 

 larly bifacial, resembling that between the oval stem-joints of 

 Plalycrinus. The brachials are single, axillary, and abut later- 

 ally against each other. The arms are long, rather stout, rounded, 

 and composed of short, cuneate pieces. Pinnules strong. 



The mode of union between the plates of the calyx is variable. 



