300 FreLp CotuMBIAN MusEumM — GEovoey, Vot. II. 
the radial plates. The diameter of the dorsal cup at the arm bases 
is about one-half greater than the height of the cup. The dorsal cup 
is ornamented with series of prominent rounded: ridges. The ridges 
begin near the middle of the lower margins of the basal plates at the 
juncture with the column and extend to the center of the plate.. 
At this point they bifurcate and pass to the center of the radials 
where they join the ridges from the basals on either side. From 
the center of the radials the ridges follow the median line of the radials 
and costals to the middle of the axillary costal where they again bifur- 
cate and follow the distichals up to the arm bases. Another, less 
conspicuous ridge connects the centers of the posterior lateral radials 
crossing the first anal plate. Surface of all plates, not ornamented with 
the ridges, smooth and moderately convex. Sutures not situated in 
grooves. In the natural casts the dorsal cup is broad and flat at the 
base and curves abruptly upward at about the middle of the basal 
plates; it expands moderately up to the middle of the radials, where 
a slight constriction occurs, and above this constriction the expansion 
is very rapid until at the arm bases the plates are nearly at right angles 
to the axis of the calyx. Ventral disc not preserved. 
Infrabasals five, small, scarcely extending beyond the columnar 
facet. Basals five, large, forming with the infrabasals a shallow cup; 
the posterior basal is heptagonal and larger than the others which are 
hexagonal. Radials five, larger than the basals; the two posterior 
laterals are hexagonal and the rest are heptagonal. First costals 
hexagonal, less than half the size of the radials. Second costals 
axillary, pentagonal or hexagonal. In some cases the interdistichal 
appears to join the axillary costal. Distichals two or more in each 
series. First interbrachials are hexagonal, intermediate in size between 
the radials and first costals; they are followed by three or more rows 
of two plates each, diminishing in size upward. Interdistichals pres- 
ent, but in the specimens at hand only the first plate is preserved; 
this appears to be hexagonal or heptagonal. The anal interradius 
is wider than the interbrachial areas. The first anal plate is hexagonal, 
smaller than the radials; it rests on the distal edge of the posterior 
basal and separates the posterior lateral radials; it supports on its 
distal edge a row of plates, diminishing in size, which lead up to the 
vault; the space between this row of plates and the posterior lateral 
rays is filled with smaller plates. 
In its general form and proportions this species is so unlike all other 
species of this genus that it will be easily recognized. 
The type specimen, P 8891, was collected by the writer in the spring 
of 1906. It consists of a nearly perfect natural cast of the dorsal 
