290 PROCEEDINGS OF THE ACADEMY OF [1879. 



boniferous it attained the maximum in length, and the cylindrical 

 form prevails, but this by degrees changed into the club-shaped 

 form, from which in the succeeding geological epochs, toward the 

 close of the Subcarboniferous, those monstrous balloon-shaped 

 sacs were developed, and with these, as if a culmination had been 

 reached, the family actually terminates. The few forms which 

 still survive can no longer be considered as true types of the 

 Cyathocrinidse. They are of a type prophetic of a new family 

 which is soon to appear, and of which Encrinus is the leading 

 genus. The resemblance of Stemmatocrinus to Encrinus is in- 

 deed so strong that one may well hesitate in which of the two 

 families Cyathocrinidoe or Encrinidai it should be classed. 

 We should probably have decided in favor of the latter, if we had 

 seen any possibility of separating Stemmatocrinus from Eupa- 

 chycrinns, and Eupachycrinus from Poteriocrinus, and so on. 

 The only real difference which we notice between the two is that 

 in Encrinus the three rings of plates which form the calyx, in the 

 Cyathocrinidae constitute an almost flat disc, or so shallow a cup 

 that there would be no space for a visceral cavity if covered by 

 solid plates, and, as no trace of a ventral covering has ever been 

 observed, it is very probable that Encrinus belongs to the Stoma- 

 tocrinoidea. 



The free floating Agassizocrinus (Astylocrinus Roemer) is an- 

 other form, in regard to which doubts might be entertained 

 whether it ought not to be ranked with the Cyathoerinidoe. Its 

 younger stage, wherein it was pedunculate, agrees well in general 

 structure with Eupachycrinus, and is very appropriately called 

 the Cyathocrinoid form. We think it better, however, to separate 

 the genus by itself, as in the case of Pentacrinus and Comatula, 

 and to place it under Aslytocrinidae. in a distinct group. 



General Family Diagnosis. Calyx composed of only three 

 rings of plates alternating with each other, each ring composed 

 of five plates; all succeeding plates free. The proximal ring or 

 underbasals not unfrequently hidden from view by the column, 

 perhaps in some cases wanting, rarely anchylosed so as to form 

 three plates or a single one. The plates of the second ring gener- 

 ally varying in form, the posterior one frequently truncate. Those 

 of the third ring or the radials, more or less pentagonal, the right 

 posterior one often smaller on account of interposed anal plates. 

 The succeeding order of plates which have been generally desig- 



