128 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
in Aybocrinus, and R in Anomalocrinus, homologous with the plate of Den- 
drocrinus, Homocrinus, etc., which is supported by #’ and partly by the 
basals, and also with the plate of Poteriocrinus, which rests upon the basals 
and against the radianal #’? This question was not discussed by Bather, 
though we had expressed views different from his respecting the plate z in 
Tocrinus and Merocrinus. That plate was regarded by us, in both genera (in 
Tocrinus as early as 1879),* as a plate of the tube, and, so far as we know, 
we never made any statement from which he might infer that we thought it 
represented the plate x; yet he quotes us in his diagrams as if we had done 
so in 1879. 
Instead of commencing with the earliest forms, as Bather did, we begin 
with the simplest, and select as a starting point the genus Cyathocrinus, which 
is so well known to every paleontologist. Cyathocrinus has simple radials, 
and but one anal plate, which, as all writers agree, represents the plate z. It 
rests upon the truncated upper face of the posterior basal, between two ra- 
dials, and is generally followed by three plates of the tube (Fig. 3), of which, 
as in the Batocrinide, the two at the sides rest to an equal extent against 
—or rather upon— the sloping upper faces of adjoining radials. The 
structure of Graphiocrinus de Kon. and Le Hon, as amended by us in 1879, is 
similar to that of Cyathocrinus. This genus also has only the plate x repre- 
sented, but here it is angular at the upper end instead of truncated, and 
supports but two equal plates of the tube. This produces a sort of bilateral 
symmetry in the posterior side of the tube, each plate supporting a vertical 
row of hexagonal or subquadrangular pieces. 
Next in order we take Dendrocrinus, in which the right posterior radial 
is compound, and its two plates are in line vertically. This genus is an 
intermediate form between the earlier and later Fistulata, and its strue- 
ture throws important light upon the phylogeny of the group, especially 
as to the anal plates. Contrary to the rule in most of the earlier Fistulata, 
the plate « is well represented, but the inferradial, 7’, is not in a posit:on to 
perform anal functions. 
Let us examine the form represented by Dendrocrinus Casei, from the 
Lower Silurian of America (Fig. 13), a species with rather narrow, horse- 
shoe shaped radial facets, and an extremely large ventral sac. The two 
posterior radials are widely separated, and the plate x is succeeded, as in 
Cyathocrinus, by three plates, t, ¢, 4, of which the middle one rests upon the 
* Revision, Pt. I., p. 65. 
