CALAMOCKINUS DIOMED.E. 39 



Carpenter is now of opinion that the ventral plates of the Camerata are 

 in their essential characters nothing but more or less highly developed 

 perisoniic plates. He has long believed this about Glyptocrinus, Reteo- 

 crinus, and similar forms. Recent work on Encrinus, Apioorinus, and Cala- 

 mocrinus has led me gradually to disbelieve in any vault as a system of 

 plates distinct from a disk. When a distinct line of covering plates mark- 

 ino- the ambulacra is not traceable, as in E. Bi'iareus and A. Roiyssianus, 

 this is not due to the ambulacra being subtegminal, as frequently asserted. 

 The real cause, I am convinced, is not this, but that the covering plates 

 are not clearly differentiated from the other plates of the disk. 



Carpenter also says that the vault of a Platycrinoid (Chall. Rep., p. 180) 

 corresponds collectively to the oral, interradial, ambulacral, and anambula- 

 cral plates of Neocrinoids, and that (Chall. Rep., p. 171) the so called vault 

 of the genus Marsupiocrinus* is really the strongly plated ventral perisome ; 

 and furthermore, that he can develop the heavy vault of the Carboniferous 

 species from the disk of the Silurian forms by a gradual course of palosonto- 

 logical development, although at the same time other lines o£ development 

 may be going on ; and finally, that the radial dome plates of the Actino- 

 crinida? are to be regarded as extravagantly developed covering plates, 

 and that the term calyx interradials should be given up. 



Carpenter and Wachsmuth and Springer are now fully prepared to admit 

 that all the plates between the rays are parts of one and the same system, 

 wliether they be massive, like the first interradials of Guettardicrinus, or 

 delicate, as in the recent PentacrinidiB. 



As has been stated by Carpenter, in the recent Crinoids thus far described, 

 they all with the exception of Thaumatocrinus have the first radials united 

 so as to form a complete ring all round the calyx ; but in that genus the 

 primary radials are separated by an interradial resting upon the basals 

 below. These calyx interradials, as they have been called, are very gener- 

 ally present in Palasocrinoids, and help to increase the size of the cup. 



In Belemnocrinus an anal plate separates two of the radials. In Ilexa- 

 crinus the same is the case. In the Mesozoic Apiocrinidre " there are 



* Scliluter gives excellent figures and a good analysis of Uintacriiuis (Zeitschr. d. Deutsch. Geol. 

 Ges., 1878), showing remai-kably well the gradual passage of the so called large calyx interradials into 

 comparatively small actinal plates. The same structure is repeated in the angle of each pair of arms 

 in the interpalmar spaces, the first large plate of the latter series resting upon the first two distichals, 

 exactly as the first plate of the interradiHl area rests upon adjoining first radials. The central plate, 

 without any perforation, is surrounded by a circle of five basals and five adjoining radials, with inter- 

 radials fully as large as the radials. 



