ckagin.] DESCRIPTIONS OF SPECIES. 39 
MOLLUSCS 
PELECYPODA. 
( )STREID^E. 
Genus OSTREA Linnseus. 
OSTREA Sp. 
Three imperfect valves of an ovate, thin-shelled ostreid, about H 
iches in greatest dimension, lie partly embedded on a piece of blue 
limestone obtained from the Theta, 1| miles east of Malone station, 
nd may represent Ostrea as distinguished from Exogyra and Gry- 
phsea. They are, however, incomplete in the region of the beaks 
nd their precise relationship therefore remains somewhat uncertain. 
The inflation is moderate and due almost wholly to the strongly 
ncurved border, the remainder of the valve being rather flat. 
Since in general aspect they recall species of Ostrea in the stricter, 
nd certainly at least represent it in the broader generic sense, while 
hey do not seem referable to any of the hitherto described Ostreidse 
f the Malone Jurassic, they are here provisionally listed as above. 
Gryrieea mexicana Felix. 
PI. Ill, figs. l-c>. 
Gryphcna mexicana Felix, 1891, Beitr. Geol. u. Pal. Mex., pt. 3, p. 178, pi. 
'21, figs. 30, 30a. 
Shell rather small, more or less inequilateral and cuneate; adduc- 
or seal- elongate, lightly impressed; margins of the valves not crenu- 
ated internally, the right valve very much smaller than the left, 
ounded-triangular, usually flat or exteriorly in part concave, thick- 
feed in the dorsal part; left valve triangular to crescentic-triangular, 
eeply excavated, strongly arched on the dorsal region, the posterior 
>art more prominently so than the anterior, its beak high-arched, 
trongly incurved and rather bluntly (seldom freely) hooked, usu- 
lly swinging a little backward, its posterior side strongly flattened 
r concave, the passage thence to the outer side more or less angu- 
ated or sometimes elevated as an obtuse fold, a similar but smaller 
attening or concavity being often present on the shorter, anterior 
ide, exterior side usually convex — sometimes flattish or concave — 
ntero-posterioriy and either without bordering sulci or provided 
rith an anterior or posterior sulcus or with both;, the growth-lines 
ometimes acute and imbricated, especially on the anterior and poste- 
ior slopes, but on the exterior slope often more commonly thickened 
t irregular intervals into obtuse wave-like elevations and often here 
lso swung upwards into a broad sinus. In specimens of smaller and 
