57 
and ninth marginal plates laterally expanded, twice as broad 
as those above the bridge. Profile of back considerably elevated 
and rounded, deepest in front of the bridge on second vertebral 
plate. A deep curvature above and beyond the bridge from 
the fifth to eighth lateral plates. Nuchal plate one-seventh 
longer than broad, quadrilateral : margino-nuchal plates much 
longer on the outer than the inner edge, the latter being equal 
to the breadth : margino-brachial plates quadrangular, the 
breadth of the first pair four-sevenths of the length, with the 
anterior and posterior margins equal ; second pair with the 
anterior margin nearly twice as long as the posterior : first 
pair of margin o-lateral plates very narrow, more than three 
times as long as broad, and much longer but not so broad as 
the second margino-brachial ; second and third pairs nearly 
rectangular ; fourth pair longer externally and posteriorly ; 
fifth pair quadrilateral and rectangular, slightly longer than 
broad : first pair of margino-femorals as broad as the inner 
edge, which is slightly less than the outer ; second and third 
pairs quadrilateral, longer than broad, with the inner edges 
the shorter : supra-caudals convex on the outer edge, forming 
a shallow notch at the symphysis, about two-thirds as broad 
as long, and very distinctly arched at the suture. First 
vertebral plate octagonal,* larger than the others, in conjunction 
with the nuchal, margino-nuchal, and anterior half of the first 
margino-brachial ; posterior edge deeply concave : second and 
third hexagonal : fourth-)- hexagonal (?) with the anterior edge 
twice as long as the posterior : fifth plate quadrilateral, its 
anterior edge but one-third of the length of the posterior, 
which barely touches the last margino-femoral, and is not 
perceptibly angulated. Posterior costal plates as high as the 
lower edge ; anterior plates very large, the outer edge nearly 
one-half longer than the first vertebral plate, measured along 
its central line. All the plates of the carapace densely and, 
with the exception of the marginal plates, deeply sculptured ; 
for the most part this sculpturation is most eccentric in 
character, consisting chiefly of a network of deep grooves 
enclosing nodules of many shapes and sizes 5 on the middle 
vertebral plates, however, it takes a more or less regular 
longitudinal form, while 011 the lower half of some of the 
costal plates, a tendency to a transverse ornamentation may 
be traced : plates of the plastron and bridge distinctly marked 
by a network of grooves, scarcely perceptible to the touch. 
* lu the type specimen, which is as yet unique, there is on the left 
side a small plate intercalated between the first vertebral and first costal 
plates, and standing on the anterior margino-brachial plate, but from 
an examination of the opposite facies it is evident that this is accidental. 
f This plate in our specimen is broken up into two parts, evidently 
by an accidental fracture, the hinder part being small and subcircular. 
