MORPHOLOGICAL PART. 117 



part consists of small limestone particles, or irregular plates, and was evi- 

 dently flexible ; while the conical part, which is composed of larger pieces, 

 appears to be almost rigid. Nothing is said about ambulacra, which were 

 probably not visible in the specimen. That the cone represents a short 

 ventral sac, and that the affinities of the Encrinidae are with the Fistulata, 

 and not with the Apiocrinidae and other Neozoic Crinoids as heretofore, 

 supposed by Miller, Miiller, Zittel and Carpenter, is clearly shown from 

 Wagner's description. 



Among Apiocrinidse de Loriol observed the tegmen in Apiocrinus roissy- 

 anus,^ a species with large, massive plates interposed between the rays, and 

 in which the plates of the cup gradually pass into the tegmen, which consists 

 of rather heavy plates. The interbrachial plates were regarded by Carpenter 

 as ^^ calyx" interradials, i. e. homologous with the interbrachials of the Acti- 

 nocrinidae, the plates of the tegmen, however, as '' disk " plates, — a position 

 which was controverted by us.f We asserted that if those plates were 

 " calyx " interradials, they should be followed by a " vault ; " but if the 

 tegmen was a disk, then the plates between the rays also had to be con- 

 sidered as disk plates. We came to this conclusion upon ascertaining that 

 the plates of the tegmen form a continuation or extension of those in the 

 cup. The plates of the two hemispheres in most cases pass imperceptibly 

 from one into the other, and have the most intimate relations. 



Apiocrinus is not the only Neocrinoid genus as to which there have been 

 doubts respecting the homologies of the interbrachial plates. Guettardicrinus 

 is morphologically in exactly the same condition, and the recent genus Thau- 

 matocrinus has ^ye large plates interposed between the radials, resting upon 

 the basals, and followed by very minute, irregular pieces, which gradually 

 pass into the tegmen. Also in many of the Ichthyocrinidae the plates be- 

 tween the rays are large and heavy; while those of the tegmen are ill-formed 

 and unusually small. Gli/ptocmus has minute, irregular pieces in the teg- 

 men, and well defined and regularly arranged plates in the cup. In all these 

 cases Carpenter took the larger plates to be " calyx interradials," but called 

 the others " disk plates," although the former occupy relatively the same 

 position as the smaller ones, and as the disk plates of the Comatulae, Calamo- 

 crinus, and the PentacrinidDe. Our recent studies show plainly that neither 

 the condition of these plates, nor the presence or absence of the ambulacra 



* Paleont. Pran^., Ire serie ; Anim. Invert., Crinoides, p. 272. 

 t Revision, Part III, pp. 63, 72, aud 137. ^ 



