Fauna of the Morrow Group 
109 
tudinally; length of arm about 25 or 30 mm., maximum diameter, 
near the mid-length, about 5 mm., diameter at either end about 
half that at the middle; plates composing the arms varying in 
height from 2 to 3 mm., end surfaces plane, united by close 
sutures, lateral surfaces bearing coarse granular pustules with 
the exception of the ambulacral surface which is smooth ; ambu- 
lacral groove about 0.5 mm. in width and depth, cover-plates 
not discernible, nerve canal central; no indication of pinnules 
present. Dorsal cup unknown. 
Remarks. In none of the specimens for which this species is 
erected is the articulating facet by which the arms were united 
to the radials preserved. Where broken^ the arms have frac- 
tured irregularly across the plates except in one specimen where 
the fracture follows the suture between two plates. The arms 
are evidently the most readily preserved portion of this crinoid 
and so far as known are unique in their structure. 
Horizon and locality. Morrow formation: near Ft. Gibson, 
Oklahoma (Stations 296 and 301). 
Crinoid plates. 
Plate II, figures S-J^a. 
In addition to the isolated plates from a dorsal cup which 
have been described above as Eupachycrinus cf. magister there 
are in the Morrow collections a number of primibrachial plates 
which are of considerable interest. They may be roughly 
grouped into two classes, a larger bulbous variety illustrated 
in figures 3 and 3a of Plate II, and a smaller spinous type 
represented by figures 4 and 4a of the same plate. The former 
group includes two specimens, both from the Brentwood lime- 
stone (Stations 147 and 210), which may perhaps belong to 
the same species which furnished the isolated basal and radial 
plates found at the latter locality. The smaller, more spine- 
like variety is present in considerable numbers in the collections 
from the Morrow formation made at Stations 296 and 301. It 
is possibly to be referred to Delocrinus dubius. 
