1886.] NATURAL SCIENCES OF PHILADELPHIA. 2ll 



out a single Palseocrinoid in which the peristomial area was 

 closed by five plat^, and therefore regard the case of Stephano- 

 crinus of the utmost importance, not only as confirming our 

 suggestions, but as throwing light upon the orals of the Palseo- 

 crinoidea generall3\ Before, however, we discuss this question 

 any further, it will be necessarj^ to point out the relations of 

 Stephanocrinus with other Crinoids. 



Stephanocrinus, undoubtedly, is closely allied to Allagecrinus, 

 Haplocrinus and Pisocrinus, and must be placed with them among 

 the Larviformia, but, owing to marked difl'erences in the form and 

 arrangement of the arms, it cannot be arranged either with the 

 Haplocrinidaa or Symbathocrinidae, and it will be necessary to 

 establish for it a separate family. Except in the arm structure, 

 the affinities seem to be particularly close with Pisocrinus, 'which 

 has similar interradial processes, formed likewise by the extended 

 limbs of the radials ; but as we know little or nothing of the oral 

 plates and ambulacral structure in this genus, a critical comparison 

 is difficult. It differs also from Haplocrinus in the position of the 

 disk-ambulacra, which in the latter are subtegminal, in the other 

 exposed to view. This, we explain b}- individual growth, and 

 assert from palseontological evidence that Stephanocrinus, like 

 Cyathocrinus and other Palseocrinoidea in its younger state passed 

 through stages in which it closely resembled Allagecrinus and 

 Haplocrinus. Admitting this, it will be interesting, and in- 

 structive, to transform theoretically the lower diffei*entiated 

 Haplocrinus, so as to conform with the conditions of the adult 

 Stephanocrinus. To this end we open out the five ventral plates 

 of Haplocrinus, so as to expose their ambulacral skeleton, and 

 push the ambulacra and the oral plate, which latter occupies the 

 central portions of this skeleton, in an outward direction, in such 

 a manner that the covering pieces fill up the clefts between the 

 interradial plates, and the oral plate the centre, increasing in size 

 as the space gradually grows larger. Nothing further is neces- 

 sary to complete the structure of Stephanocrinus but to extend 

 the sides of the interradials laterally, so as to close the ambu- 

 lacral groove from beneath. By these manipulations, in which, we 

 think, we closely imitated the natural development as it took 

 place among Palaeocrinoids palgeontologically, we placed the two 

 genera in the same relative position, in hopes to arrive therebj' at 



