120 TROCEEDINGS OF THE ACADEMY OF [1886. 



plates. Those of the second circlet have been regarded all five as 

 radials, and the calyx to the top of the radials as being perfectly 

 symmetrical. It looks to us unreasonable, when we compare 

 Baerocrinus with Hoplocrinus and Ryboc7'inus, and finding their 

 structure in other essential points almost identical, that. the one 

 genus should be almost perfectly symmetrical, the other e'x- 

 tremely irregular. And, therefore, it is probable that one of the 

 nyn-armbearing so-called radials represents an azygous plate, such 

 as we find in most of the Fistulata, that the right posterior radial 

 and the anal plate were as yet undeveloped, and that Baerocrinus 

 had but four radials. This interpretation of the plates, it seems to 

 us, is corroborated by the gradual ^disappearance of the azygous 

 plate among allied forms in pala^ontological times, and b}^ the 

 contemporary increase in the dimensions of the right posterior 

 radial and the anal plate. The two latter pieces probably were 

 absorbed from the azygous plate : at first the posterior radial, 

 which in Hoplocrinus took the right upper corner, the left side 

 remaining intact ; afterwards in Hybocrinus the anal piece, which 

 absorbed the left corner of the plate also.^ 



All this goes to prove that Baerocrinus represents a very low 

 organization, or is, according to P. H. Carpenter, " a permanent 

 larval form." 



Revised Generic Diagnosis. Form of the calyx cup- or goblet- 

 shaped. Underbasals wanting. Basals five, subequal and com- 

 paratively large, 



Radials large, irregular, only four of them developed, the right 

 poster o-lateral one absent. Three of the plates equal, the fourth 

 one narrower. A large az3'gous plate occupies the same range 

 with the radials and, like these, rests alternately^ upon the basals. 

 It is undivided, and resembles the radials in form. In the type 

 specimen onlj' three of the radials are arm-bearing, the smaller 

 one not having even an arm-facet. Arms five, simple throughout, 



^ In our paper on Hyhocrinus, Hoplocrinus and Baerocrinus, we stated 

 that probably the azygoiis plate of the latter was liomologous with the 

 anal plate as represented in the larva of Aniedon. In making this state- 

 ment we had overlooked the fact that the latter plate is simply an inter- 

 radial with special function, while the azygous plate in Baerocrinus is as 

 much radial as interradial. They both agree, however, in being absorbed 

 by other plates ; the azygous plate palseontologically by the right posterior 

 radial and anal plate, the other in the growing animal over the whole 

 surface. 



