CALYPTOCRINID&. 3845 
Basal concavity a little wider than the column, and rather deep, the basal 
plates occupying almost its whole width. Radials curving abruptly inward 
at the lower end, forming a sharp edge at the bottom of the dorsal cup; the 
exposed upper part wider than long, and nearly as large as both costals to- 
gether. First costals once and a half as wide as long; the second a little 
wider and pentangular. First distichals almost as large as the costals, the 
second one third smaller, and the arm-bearing palmars about half the size of 
the second distichals and pentangular. First interbrachial large, subcircular 
in outline though actually decagonal ; it meets the two succeeding plates, 
which are as long as the first, and near the lower end almost as wide; the 
upper parts tapering rapidly to a rather sharp point, which rises to the height 
of the fourth arm pieces. Interdistichal narrower and shorter than the two 
upper interbrachials ; the lower end angular and barely touching the upper 
angle of the adjoining costal; the projecting upper end narrow and truncate. 
Compartments for the reception of the arms deep; the partition walls thin 
throughout, their width at the lower end half that of the arms, the outer faces 
flat. The summit closed by a small rosette of about eight pieces without 
additional plates. Arms very gradually tapering, the outer face slightly 
convex ; they are composed of moderately short pieces, which interlock 
from the fourth plate. With the exception of the partitions nothing is 
known of the construction of the disk. Column round, the nodal joints 
high and cylindrical, the younger joints a little narrower; axial canal 
pentalobate. 
Horizon and Locality. — Niagara group ; Waldron and Hartsville, Ind. 
Types in the American Museum of Natural History at New York. 
Remarks. — This species has such close affinities with 2. crassus that it 
might be taken for its younger stage; but on close inspection it will be ob- 
served that the specimens have all the characteristics of an adult form. The 
arms not only are biserial, but their plates are almost transversely arranged. 
Moreover, the arms are placed deeply in between the projecting upper ends 
of the interbrachials and interdistichals ; only in young specimens the tips 
are almost on a level with the distal faces of the arm-bearing palmars. It 
differs from Z. crassus in its much smaller size, being only from 12 to 22 
mm. in length by from 10 to 15 mm. in width, in the more evenly ovate 
form of the crown, in not being truncated at the lower end, and in having 
much shorter costals, and proportionally larger and pentangular arm-bearing 
palmars, 
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