50 
EOCENE TESTDDINATA. 
sculpture is a honeycomb, where the fossaj are wider than the separating- 
ridges, which is travers'ed at intervals of two or three fossse by elevated 
lines, which are transverse or oblique to the long axis of the costal bones 
as they are situated in the carapace. These lines are elevated portions of 
those separating the fossaj, and hence differ entirely from the smooth, thick 
-welts of the species of the genus which follow. They are usually zigzag 
in their course, as defining the pits, and sometimes inclose small pits. The 
vertebral bones are strongly pitted. None of the specimens indicate large 
size. 
Measurements. 
Width of a vertebral boue. 
Width of a costal bone. 
Thickness of the same. 
Interval between two raised lines. 
M. 
0. 0J2 
0. 022 
0. 005 
0. 007 
II .—Sculpture coarsely or finely punctate : 
Plastomenus communis, Cope. 
Plato xsv, tigs. 1-6. 
System. Cat. Vert. Eocene New Mexico, U. S. Geog. Snrvs. W. 100th M., 1875, p. 35. 
Carapace coarsely pitted in transverse lines, the surface crossed trans¬ 
versely, obliquely, or longitudinally by uninterrupted welts. 
The typical specimen of this species is of considerable size, and 
embraces the greater part of the carapace in a fragmentary condition. 
There are portions of three other individuals of similar proportions, and 
jiarts of four other smaller ones. Of the latter, two, which I refer to as 
var. II, are disproportionately thin, so as to occasion question of their 
proper reference here; while two others, still smaller, are relatively stouter, 
so as to render it probable that they are young animals of the P. communis. 
The typical specimen, as well as the stouter ones referred to it, is 
characterized by an increase of thickness to the free border of the carapace, 
which is unusually obtuse and heavy. No rib-extremities project beyond it. 
Measurements. 
Width of a costal bone.. 
Thickness^at the border of the same. 
Five pits in. 
M. 
0. 044 
0. 012 
0.010 
