362 PROCEEDINGS OF THE ACADEMY OF [1890. 



A similar porous sue is found in the Heterocrinidae and Belenino- 

 crinidae, but nothing is known of the other phates of the disk. 



Among the Encrinidae, a ventral pavement has been discovered 

 by Wagner (Zeitschr. d. Deutsch., Gesellsch., 1887, pp. 822 to 828). 

 The pavement, as we infer from his description, rests against the 

 radials, whence it I'ises to about the height of the third brachials, 

 where it coutracts abruptly to one-half its diameter at the base, and 

 is surmounted by a sort of cone. The peripheral part consists of 

 small limestone particles or irregular plates, and is decidedly 

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

 is more or less rigid. Nothing is said about the ambulacra, which 

 probably were not visible in the specimen. That the cone represents 

 a short ventral sac, and that the Encrinidae must be classified with 

 the Fistulata, as we have always maintained, is clearly shown from 

 Wagner's description. 



A somewhat similar disk has been observed by De Loriol in Apio- 

 crinus roissyauus (Paleont. Francaise., 1st serie, Anim. Invertebr., 

 Crin., p. 272), a species which is here of especial interest as having 

 plates interposed betweeen the rays. These plates, Avhich are large, 

 extremely heavy, and apparently rigid, w^ere regarded by Carpenter 

 as true " calyx interradials." Upon this we criticised him (Revision^ 

 Pt. Ill, pp. 63, 72 and 137), as it appeared to us the plates must re- 

 present morphologically the same thing as the smaller plates between 

 the rays of the Pentacrinidae and Comatulidae. They occupy not 

 only a similar position, but also join with the plates of the ventral 

 disk in a similar manner. A structure parallel to that of Apiocrinus 

 roissyanus, we find in most of the Ichthyocrinidae and in Guettardi- 

 crinus. The interradials are large and heavy, rather regularly ar- 

 ranged, and it was the superficial resemblance that led Dr. Car- 

 penter to regard them as homologous with the calyx interradials of 

 an Actinocriuoid, and as morphologically distinct from the plates be- 

 tween the rays of the Comatulidae. This leads to the question what 

 are "calyx" and what "disk" — interradials? The former term 

 was introduced by Carpenter, but so far as we know^, never explained 

 by him. 



It has been our impression that in all Crinoids with a vault, i. e., 

 all forms in which we supposed we found a subtegminal disk, or had 

 reason to postulate a disk from analogy, the plates between the rays 

 invariably were " calyx " interradials ; and, on the contrary, in those 

 Crinoids in which the disk itself formed the surface, all plates between 



