WHITE.] CRETACEOUS FOSSILS. 13 
EXOGYRA FORNICULATA White. 
Plate 14, figs. 2a and b. 
Gryphea pitchert Marcou, 1858 (not Morton), Geol. of N. A., pl. iv, figs. 5 and 6. 
Gryphea navia Gabb, 1861 (not Conrad), Proc. Acad. Nat. Sci. Philad., p. 22; ib., Paleont. 
California, vol. ii, p. 2738. 
Exogyra forniculata White, May, 1880, Proc. U. S. National Museum, vol. ii, p. 293. 
Shell of moderate size, subtrihedral in lateral outline, somewhat com- 
pressed vertically; under or left valve thick, especially its umbonal 
half; beak curved strongly towards the posterior border and in the plane 
of the free margins of the valve, not forming so much as one complete 
volution, its point being free but closely approaching the posterior bor- 
der of the valve; ligament-area irregularly triangular, moderately large, 
extending to the apex of the beak, its sulcus well developed; interior 
surface having the usual characteristics of the genus. A faint, illy-de- 
fined sulcus is apparent on the posterior portion of the surface, extend- 
ing from the umbo to the basal border, between which sulcus and the 
laterally flattened-concave posterior border of the valve there is an 
equally indefined radiating curved ridge. The anterior portion of the 
valve is marked by a strong, angular, rough carina, or ridge, which ex- 
tends from the beak to the basal border. The prominence of this ridge 
gives a flattened aspect to the outer surface of the valve and also pro- 
duces a flattened space of considerable width between it and the an- 
terior margin. Surface marked by the ordinary coarse lines and imbri- 
cations of grewth common to the Ostreide, and upon the ridge just 
described there are occasional nodes, or vaulted projections of portions 
of the shell. Upper vaive flattened and having much the aspect of that 
of a Gryphea. 
Length, 70 millimeters; breadth across the base, where it is widest, 
50 millimeters. 
This shell is much like a Gryphcea in general aspect, but it is referred 
to Exogyra because of its laterally-curved umbo and beak. It is often 
difficult to point out clear distinctions between these two genera, but the 
lateral curvature of the beak appears to be the most constant and im- 
portant characteristic of Hxogyra, distinguishing it from Gryphea. Spe- 
cifically, this shell is well marked by the strong, rough, angular carina, 
its free beak, narrow umbonal region, and broad base. In these respects 
it differs too much from any described species except a variety of Gryp- 
hea pitcheri, to make detailed comparison necessary. 
Morton’s Gryphea pitcheri has, unfortunately, been the cause of much 
controversy among paleontologists, in which the species here described 
has been involved because of some general resemblance which it bears 
to some varieties of the former. It is not my purpose to add anything 
to that controversy, but to endeavor, by the following remarks, to free 
Hxogyra forniculata from necessary connection with it. 
Professor Marcou (loc. cit.) referred this species to G. pitcheri, and 
gave excellent figures of it, but it differs materially from any of the sev- 
eral varieties of G. pitcheri in (not to mention other features) the invari- 
able lateral deflection of the beak. If Gryphwa be distinct from Hxogyra, 
then this is a generic character; and, in any case, it is at least a strong 
specific one, aud one which is constant and readily recognizable. 
Mr. Gabb (loc. cit.) referred this species to G. navia Conrad; and on 
p. 274 of the last-cited work he gave a new name, G. mucronata, to the 
true G. navia, or to a form that its author cited as such. Mr. Conrad 
