148 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



the radial symmetry, but the bilateral as well, and strongly suggest that 

 the Crinoids had to wrestle for a long time with the tendencies derived from 

 their Cystid antecedents, manifesting themselves in a variety of irregular- 

 ities, which from time to time characterized special groups. Such are the 

 presence of compound radials in one or more rays; the variations in the 

 form and composition of the proximal ring in the base ; the non-arm bearing 

 radials of Baerocrinus, Atelestocrinus, and Trihrachiocrinus ; the irregular 

 number of radials — more or less than five — of the Plicatocrinidse ; and 

 the almost complete obliteration of symmetry among the Pisocrinidse and 

 Calceocrinidse. 



The division of the Crinoids into two orders : " Palaeocrinoidea " and 

 "Stomatocrinoidea" was proposed by us on account of the apparent difer- 

 ence in the conditions of the actinal portions of the calyx, whereby mouth 

 and food grooves, and the ventral disk generally, of all Palseozoic Crinoids, 

 without exception as we supposed, was covered by a special integument — 

 the "vault" of antecedent literature — instead of being external and exposed 

 to view. With the knowledge we then had this seemed to be a character 

 morphologically of extreme importance, and it was so regarded by others. 

 Under the order Palaeocrinoidea we placed all Crinoids with covered mouth 

 and closed food grooves, and under the Stomatocrinoidea those in which 

 mouth and food grooves are exposed. The two groups were accepted by 

 Carpenter, but he changed the name of the latter into "Neocrinoidea." 



Another classification was introduced by Neumayr,* who proposed the 

 name " Hypascocrinoidea " for all Crinoids in which mouth, ambulacral 

 vessels, and 8aumpldttchen (the latter if present) are beneath the tegmen ; 

 and the " Epascocrinoidea " for those forms in which the ambulacra are not 

 covered by the tegmen, but have external grooves, which are either exposed 

 or closed by movable SaumioldttcJien. Under the latter he arranged all recent 

 Crinoids with our Fistulata; imder the former the Ichthyocrinidge and Haplo- 

 crinidse together with our Camerata. It is surprising that Neumayr's classi- 

 fication, while based like ours upon the condition of the mouth and surround- 

 ing parts, led to such different results. This must be attributed largely to 

 the interpretation which he gave to the disk of Cyathocrinus, in which he 

 took the vacant space found in the centre of imperfect specimens for the 

 mouth, and to the fact that he was unacquainted with the ventral structure 

 of the Ichthyocrinida3. 



* Die Stamme des Thierreiches, 1889, p. 462. 



