12G rROCEEDINQS OP THE ACADEMY OF [188G. 



joints, the ambulacra resting almost exclusively against the dorsal 

 side of the calyx. 



Eybocystites is one of the earliest and lowest forms of the 

 Palseocrinoidea ; it may be regarded as a permanent larval form 

 of Hybocrinus, which had no arms, but in their place food grooves' 

 upon the dorsal side of the calyx. It is interesting that in this 

 case as in that of Baerocrinus, which has similar relations to 

 Hoplocrinus as this has to Hybocrinus, three of the rays are some- 

 what higher developed than the two others. 



We propose the following : 



Revised Generic Diagnosis. Eybocystites agrees with Hybo- 

 crinus in its general form, the arrangement and proportions of 

 the plates in the calyx, in the ventral covering, and in the form 

 and size of the ventral sac, but differs from that genus essentially 

 in the arm structure. It has no underbasals ; five large subequal 

 basals, five radials, one of them much smaller and resting upon 

 the right sloping upper side of the large azygous plate. The 

 latter supporting at its left sloping side an anal plate, in form 

 resembling the adjoining small radial. Arms rudimentary, of 

 the most primitive kind, restricted to the two posterior raj's and 

 the anterior one. They consist, so far as known, of two quad- 

 rangular joints, which are united with the radials by close suture. 

 The joints are provided with an ambulacral furrow, which enters 

 the calyx apparently at the top of the radials as in Hoplocrinus. 

 This furrow passes from the ventral side of the two arm joints, 

 over the top of the upper one, and follows the dorsal side of the 

 plates until reaching the calyx, whence it extends upon the sur- 

 face of the radials to the basals, either entering them or terminat- 

 ing close to the basi-radial suture or along the face of the large 

 azygous plate. The two antero-lateral rays have no arm plates 

 whatever, but each is provided with an ambulacral furrow, pass- 

 ing out from near the top of the radials, traversing these plates, 

 and entering the basals. There is considerable irregularit}^ in 

 their position and length, but as a rule these latter furrows enter 

 deeper into the basals than those of the three other rays. The 

 furrows are provided with two rows of side pieces which are 

 arranged in the usual way. 



Ventral sac short, as in Hybocrinus^ provided along its ventral 

 gide with a small anal opening. Column circular, small. 



