ckagin.] DESCRIPTIONS OF SPECIES. 41 
Genus EXOGYEA Say. 
EXOGYRA SUBPLICIFERA Felix. 
PI. IV, figs. 1-4. 
Exogyra subplicifera Felix, 1891, Beitr. Geol. u. Pal. Mex., Pt. Ill, p. 177, 
pi. 27, figs. G, 7. 
From locality H miles east of Malone station, and associated with 
nost of the commoner fossils described in this paper, were collected 11) 
pecimens, besides 8 obtained by Doctor Stanton. Two somewhal 
loubtful casts were also found, with Gryphcea mexicana, A*starte 
nalonensis, etc., just above the beds of conglomerate, at the eastern 
mse of Malone Mountain, in the anticline about 1 mile north of the 
southern end of the mountain. 
The shells occur both free, or nearly so, and attached by nearly the 
vhole of the left valve. The largest example from the Malone Hills 
las a length of 35 mm., but some of the smaller ones agree nearly in 
ize with the Mexican specimens described and figured by Doctor 
Jelix from the Cerro de Titania. The right valve has the beak 
trongly recurved laterally, and sometimes has the anterior dorsal 
>order drawn across the uinbonal cavity so as to form more or less of 
cul de sac, and in the more nearly free examples is rather thin, 
leeply excavated, and ornamented with numerous imbrications which 
)resent distally an obtuse angle on the summit of convexity, and in 
ome of the young examples may have. 1 to 4 faintly expressed radial 
? olds on the basal part. In young specimens the right valve is more 
>r less triangular, broad across the distal part, and a little produced at 
he base; in the adult it usually becomes auriform. 
The following is a translation of the original description by Doctor 
^elix, relating to the right valve, which is exceedingly characteristic 
nd on which alone the species was established: 
It is of auriform — sometimes rather elongate, sometimes more broadened — 
•ontour, like the Cretaceous E.rogyra auricularis Brongn. sp., which lias been 
■egarded by Coquand as a variety of his /;. plicifera. On its inner surface it 
tears a variable number, mostly 5 to 8, of transverse folds, which are in strong 
■elief, but do not extend across the entire shell breadth, by which sculpture it is 
specially distinguished from related forms. It may be taken for granted that 
f adult examples show this sculpture on their inner side, free or only umbonally 
dnate individuals will show it on their outer surface in at least as distinct a 
nanner as the Cretaceous E. plicifera Coqu. possesses it. 
The length of the specimen in the middle amounts to 15 mm. 
Exogyra potosina C. and A. 
PI. Ill, fig. 7; PI. IV, fig. 7. 
Exogyra potosina Castillo and Aguilera, 1895, Faun. Foss. Sierra d. Catorce, 
p. 3, PI. II, fig. 9. 
Doctor Stanton's collection contains six specimens that are referred 
o this species. All are larger than the Mexican type specimen fig- 
