1888.] NATURAL SCIENCES OF PHILADELPHIA. 337. 



DISCOVERY OF THE VENTRAL STRUCTURE OF TAXOCRINUS AND 



HAPLOCRINUS, AND CONSEQUENT MODIFICATIONS IN 



THE CLASSIFICATION OF THE CRINOIDEA. 



BY CHARLES WACHSMUTH AND FRANK SPRINGER. 



Since the publication of our paper "on the Summit Plates of 

 Blastoids, Crinoids and Cystids, and their Morphological Rela- 

 tions," ^ we have made several important discoveries bearing on this 

 subject, which have materially modified some of the views expressed 

 therein, as well as at some places in the Revision of the Paloeocri- 

 noidea. 



Hitherto we have recognized in the summit of the Palseocrinoids 

 a central plate, surrounded by four large jDroximals and two small- 

 er ones, with anal plates interposed between them. In our earlier 

 writings we regarded the two small proximals as representing pos- 

 teriorly a fifth plate; but these, as we have explained (Revision Pt. 

 Ill, p. 47), are really the two posterior radial dome plates, pushed 

 in by the anal structures, the three other radial dome plates being 

 placed at the re-entering angles of the four larger proximals. This 

 was clearly pointed out on PI. VII, in figures 2, 3, 4, 5, 6, 8, 9, 10, and 

 on Plate VIII, figs. 1, 3, in which the plates formerly considered as 

 the smaller proximals were marked as actinal radials, and designated 

 by the letters "x r." In fig. 7, PI. VII, they correspond to, and prob- 

 ably are, the first or inner covering pieces of the ambulacra. After 

 discovering that these plates are situated radially and not inter- 

 radially, we met with frequent difficulty in identifying the two small- 

 er proximals, and mistook for them some of the plates which we 

 now clearly see are anal pieces. In some cases, and especially in 

 veiy complicated forms, we observed intercalated between the prox- 

 imals, touching the central piece, certain plates which we regarded 

 as the representatives of the first and second radials of the dorsal 

 cup, absent in the vault of simpler forms ; while we considered those 

 underneath which the bifurcation of the ambulacra takes place — 

 being the radial dome plates in the simpler forms — as the representa- 

 tives of the third or axillary radials. 



From the internal structure we found that the radiation of the 

 ambulacra was from underneath the central plate, in a similiar man- 

 ner as the ambulacra from beneath the five orals in the Neocriuoidea, 



1 Proc. Acad. Nat. Sci. Philadelphia, March, 1887. 



23 



