276 



Field Columbian Museum — Geology, Vol. II. 



Interbrachial areas (I Br.*): The plates in camerate crinoids sit- 

 uated between the rays. 



Anal or posterior interradius (X. a. a.) : The area situated between 

 the right and left posterior rays and leading up to the anal opening. 



Basals (B) : The circle of plates directly below the radials and alter- 

 nating with them. In a monocyclic base they join the column. 



Infrabasals (I B) : The first row of plates in a dicyclic base. They 

 separate the basals from the column and are radial in position. 



^9^ 



'^m 



Fig. 2. Diagram of a 

 Dicyclic Crinoid. 



Fig. 1. Diagram of a Monocyclic, Camerate Crinoid. 



Radials (R) : The first plate of each ray, usually resting on the ba- 

 sals. In some families part of the radials are divided horizontally. The 

 parts of these plates are called superradials (Rs) and inferradials (Ri), 

 respectively. 



Costals (C) : Those plates of each ray extending from the radials, on 

 which they rest, up to the first bifurcation. 



Distichals (D) : All plates of each ray between the first and second, 

 bifurcation. 



Palmers (P) : All plates of each ray between the second and third 

 bifurcation. Any plates of a higher order than these are called post- 

 palmers. 



* The letters in parenthesis refer to those of Figs. 1 and 2. 



