162 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
The least departure from the structure of the Larviformia toward the 
Fistulata is found in the genus Carabocrinus, in which the tegmen is com- 
posed of five asymmetrical orals, meeting laterally and by their inner 
ends, four of them resting against the radials, the posterior one being 
separated from them by a number of irregular perisomic pieces, which 
enclose a short anal pyramid. Somewhat higher differentiated is the 
tegmen of Cyathocrinus alutaceus Angelin— C. ramosus Bather — (Plate III. 
Fig. 6), whose ambulacra are subtegminal, but the orals are separated 
from the radials by a narrow belt of perisome; contrary to other species of 
Cyathocrinus, in which the ambulacra rest upon the tegmen, and the orals 
are, or seem to be, in a state of resorption. In Hybocrinus, the ventral sac is 
as small as in Curabocrinus, and it has large orals resting against the radials ; 
but the lateral edges of the plates are covered by the Sawmpliittchen. The 
Cyathocrinide have a large ventral sac, and in the tegmen a madreporite, 
which was probably unrepresented in the Poteriocrinide, in which the sac 
itself is perforated. The ventral sac made its appearance in the Hybo- 
crinidxe, Carabocrinide, and Anomalocrinide as a very insignificant protuber- 
ance; in the Heterocrinide, Belemnocrinide, and especially in the Cyatho- 
crinidee, and Poteriocrinide, it attained enormous dimensions, but dwindled 
down in the Encrinidz to almost nothing, although some of them still have 
well defined anal plates. We do not restrict the Encrinide to forms without 
anal plates, such as Encrinus, Stemmatocrinus, and Erisocrinus ; but include 
among them the genera Lupachycrinus, Cromyocrinus, Certocrinus, and Oncocrinus, 
in which the anal area passes through all possible transition stages. We 
make the reduced size of the sac, and the highly differentiated articulation 
between the radials and brachials, the distinctive characters of the family. 
The Camerata constitute a compact and well limited natural group, and 
they are a highly specialized type, which by extraordinary development 
reached a stage of extreme differentiation, and produced a ventral structure 
apparently so different from that of other groups, that it was for a long 
time found impossible to homologize its plates with those of the other 
Crinoids. They represent a type of rapid culmination and development, 
possessing already in the earliest known forms well defined pinnules, and the 
biserial arm structure in most of their families being permanently established 
at the close of the Silurian. The organization of the Camerata may not be 
intrinsically higher than that of the other groups, but they very clearly 
represent a higher state of development than Haplocrinus or Symbathocrinus, 
