170 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
CAMERATA. 
Analysis of the Families. 
I. Typrcat SEcrion. 
Lower brachials and interbrachials forming an important part of the 
dorsal cup. 
A. INTERRADIALS 1LL DEFINED. 
The lower plates of the rays more or less completely separated 
from those of other rays, and from the primary interradials, 
by irregular supplementary pieces. Anal interradius divided 
by a row of conspicuous plates. (Dicyclic or Monocyclic) . RETEOCRINID®. 
B. INTERRADIALS WELL DEFINED. 
1. Dicycric. 
a. Radials in contact except at the posterior side . . . . . THYSANOCRINID®. 
b. Radials separated all around . . . . »« « »« »« «» « s RHODOCRINIDE. 
2. Monocyctric. 
a. Radials in contact all around. 
Symmetry of the dorsal cup, if not strictly pentamerous, 
disturbed by the introduction of anals between the 
Dm omky 5 og 5 5 6 & 0 9 6 6 o Ste 5 A MELOCRINID. 
Arms borne in compartments formed by partitions attached 
tothe tegmen. Dorsal cup perfectly pentamerous. Plates 
of calyx limited to a definite number . . . . . - . CALYPTOCRINID#. 
b. Radials in contact except at the posterior side, where they 
are separated by an anal plate. 
First anal plate heptagonal, followed by a second between 
iM) etree MY 6 6" g ob 9 6 56 6 0 56 } Oo Cc BATOCRINIDE. 
First anal plate hexagonal, followed by two interbrachials 
without a second anal. Arms branching from two main 
trunks by alternate bifureation . . . . . . . - . ACTINOCRINIDS. 
II. Non-Tyrican Section. 
Brachials and interbrachials but slightly represented in the dorsal cup. 
1. Monocyc tic. 
a. Radials in contact all around. Base pentagonal. . . . PLATYCRINID2. 
6. Radials separated at posterior side by an anal plate. Base 
hexagonal. 
Basals directly followed by the radials. . . .. . HEXACRINID®. 
Basals separated from radials by accessory pieces . . ACROCRINID&. 
2. Dicycuic. 
Radials in contact except at the posterior side. . . . . CROTALOCRINIDE. 
