94 PSEUDOCERATITES OF THE CRETACEOUS. 
This specimen, therefore, affords clear ideas of the mode of development 
of the full-grown sutures in this form and also in the group to which it 
belongs. 
Locality: Near Carthage, N. Mex. 
Age: Colorado group, Upper Cretaceous. 
COILOPOCERAS NOVIMEXICANUM n. Sp. Hyatt. 
Pl. X, figs. 1-4. 
This species appears to be more like Sphenodiscus lenticularis Meek 
than any other at first sight, but the sutures and other characters are so 
dissimilar that this impression is easily corrected. 
The cast in hand is 93 mm. in diameter and, allowing for siphuncle on 
one side and crests ou both sides, it would be, when perfect, about 96 mm. 
The transverse diameter of the outer volution is 56 mm., the umbilicus is 
about 1.5 mm., and the outer volution below on same line is 34 mm. without 
siphuncle and crest, which would make it with both about 35.5 mm. ‘The 
transverse diameter, about the middle of the lateral zone, is 23 mm. for the 
largest, oldest part of the volution and 15 mm. for the smaller, younger 
part opposite this. The latter had the shell on both sides, and deducting 
this it would be 14 mm. 
While the form and aspect were the same as in most other species of 
this genus, it has very faint fold-like coste on the outer part of the last half 
of the outer volution and more decided and more fold-like costations upon 
the younger portion and on first quarter of the exposed volution; these last 
reach to the umbilical shoulder. 
The venter is subacute, with blunted, narrow crest, and on either side 
of this lateral zones are slightly concave on the entire outer volution. The 
shell vaulted over a clear space above the siphuncle, the hollow keel, and 
this was filled by clear, crystalline limestone different from the matrix, 
and there was a black layer over the siphuncle. Farther out a part of the 
black layer was found to consist of black dendritic oxide of iron. The 
sutures are equally peculiar. Upon closer examination it is seen that the 
resemblances to Placenticeras are due to the small size of marginal saddles, 
the solidity of the fourth lateral saddles and the greater complication of 
the smaller saddles than in Sphenodiscus. There are, however, but two 
