58 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Hyocrinus and Rhizocrinus, and it is possible that the former has really but three 
basals; but in L?hizocrinus the fusion was not complete, as Count Pourtalés 
proved by inserting a needle in the central canal, whereupon the base sepa- 
rated into five pieces.* 
The foregoing facts are of considerable importance as to classification. 
For if the smaller number of plates is merely a modification of the original 
five, the number of basals cannot be regarded as a good character for sepa- 
rating the Crinoids into primary groups, as was practically done by Angelin, 
and afterwards by 8S. A. Miller. 
The basals of dicyclic Crinoids, as we have stated, invariably consist of 
five pieces, but their form differs in different groups. In the Rhodocrinide 
(Fig. 17) they are all heptagonal; while in the Thysanocrinide the posterior 
one is heptagonal, and the four others hexagonal (Fig. 18) — the former 
supporting a supplementary plate at each interradius, the latter at the anal 
side only. In the Fistulata, all five plates are hexagonal when there is no 
anal plate, as in the Encrinide; but in the Cyathocrinide, whenever that 
plate is represented, four of the basals are hexagonal, and the fifth hepta- 
gonal, precisely as in the Thysanocrinide. In the Poteriocrinid, and all 
other families in which in addition to the regular anal plate a radianal is 
represented, only three of the basals are hexagonal, and the posterior and 
right postero-lateral basals are heptagonal (Figs. 15 and 16). 
The same variations occur among the basals of the Ichthyocrinide. 
Those of Ichthyocrinus agree with the basals of the Encrinide; those of 
Mespilocrinus, Taxocrinus, Forbesiocrinus, and Calpiocrinus, with the plates of the 
Cyathocrinidx; while the basals of Lecanocrinus, Gnorimocrinus and Sagenoerinus 
are in a similar condition to those of the Poteriocrinide. 
Three infrabasals have been’ observed only among the Fistulata and 
Articulata. They are represented sparingly among the former, but are the 
rule among the Ichthyocrinide, and are represented in the larva of the 
Comatule. Wherever they occur, they consist of two large plates and a 
smaller one, which are differently arranged in the various groups. In the 
Fistulata, according to Bather, the position of the small plate is not constant ; 
we have always found it located anteriorly below the suture between the 
two anterior basals, and the plates f and g and 7 and & fused together 
(Fig. 16). In the Ichthyocrinidx, however, the small plate rests below the 
suture between the posterior and right postero-lateral basal, and / and g and 
* Memoirs Mus. Comp. Zodl., Vol. IV., p. 29. 
