412 PROCEEDINGS OF THE ACADEMY OF [1881. 



EXPLANATION OF THE PLATES. 



The folloioing letters denote the same parts throughout all the plates. 



u = underbasals. 



b ^= basals. 



r = radials (r' primary radials, r' secondary radials, etc.). 



i ^= interradials. 



d =: interaxillary plates. 

 cd = central dome plate. 

 pd = proximal dome plates. 



rd = radial dome plates [rd- = secondary radial dome plates). 

 id = interradial dome plates. 

 dd = interbracliial dome plates. 



a — arm plates. 

 fa = fixed arm plates. 

 fp ^= fixed pinnules. 



X = anal plates. 

 xd = anal dome plates. 



A ^= arms. 

 AO =: arm openings. 

 FB = free rays. 

 lA = interradial appendages. 

 EP = respiratory pores. 



H = hydrospires. 

 AT = ambulacral tubes beneath the vault. 



G = galleries beneath the vault. 



/= interpalmar spaces. 



X — anus. 



C — column. 



EXPLANATION OF PLATE 17. 



Fig. 1, Platycrinus regalis Hall. The plates in calyx and vault. 

 Fig. 2. Ollacrinus tuberculosus Hall. The plates in the calyx, and those 

 of the interradial appendages and arms. 



EXPLANATION OF PLATE 18. 



Fig. 1. Extended rim of Strotocrinus regalis (dorsal side). All plates 

 below the secondary radials broken away, exposing to view the inner 

 floor of the vault. (This figure in connection with figs. 2, 3, 4, 5, 6, 7, 

 is designed to illustrate the character of a continuous rim and of free 

 rays as extensions of the body, their relations to the arms, and the 

 derivation of the arms fi'om pinnules.) 



