892 PROCEEDINGS OF THE ACADEMY OF [1890. 



Fig. 11. Inner floor of the tegmen in Physetocrinus. 



Showing the cavernous pits and passages. The braces rep- 

 resent the thickened interradial portions, which form the 

 galleries for the reception of the ambulacr^l skeleton. 

 (Collection of "Wachsmuth and Springer.) 

 Fig. 12. Posterior or anal side of Dendrocrinus casei Meek. 

 From a specimen in the collection of Wachsmuth and 

 Springer. 



(All figures are enlarged two diameters, except fig. 9 

 which is enlarged four times, and fig. 11 which is but one- 

 half larger). 



PLATE X. 



Fig. 1. Ventral disk of Cy'athocrinus harrodi W. and Sp. 

 Showing the structure of the ambulacra, and the ventral 

 sac to its full length. 



(Collection of Wachsmuth and Springer). 

 Figs. 2 and 3. Cyathocrinus iowensis 0. and Shum. 



Fig. 2. Specimen in which only the " consolidating plates " 



are in, situ. 

 Fig. 3. Another specimen, in which the " consolidating 

 plates " are covered over by ambulacral and inter- 

 ambulacral plates ; the orals are partly resorbed. 

 (Same collection). 

 Fig. 4. Cyathocrinus longimanus Angl. 



Showing the arrangement of plates in the tube. (After 

 Angl.). 

 Figs. 5a, b. Iocrinus sub-crassus Meek and Worthen. 



a, posterior aspect ; b, portion of the ventral tube enlarged. 

 Figs. 6 to 14. Diagrams showing the relations of the anal 

 plates to surrounding parts. 



Fig. 6, in Baerocrinus ; fig. 7, Hyhocrlnus ; fig. 8, Het- 

 erocrinus hellevillensis ; fig. 9, Ectenoerbms simplex ; fig. 

 10, Anomalocrinus ', fig. 11, Dendrocrinus caduceus; fig. 

 12, Poteriocrinus ; fig. 13, Ceriocrinus ; fig. 14, Ulocrinus. 



Explanation of Lettering. 

 R. Radial. 



R'. Lower half of a compound Radial. 

 R''. The latter assuming anal functions=Radianal. 

 X. The true anal plate. 

 t. Plates of the ventral tube. 



