ORISKANY SANDSTONE. 
457 
This species varies greatly in form; some individuals being very gibbous and 
distinctly ovate, while others are more or less compressed and very elongato-oval or 
narrow elliptical : the first variety was Eaton’s Terebratula oroides , and the latter 
his T. perovalis. In the young state, the length and breadth are often equal or nearly 
equal. 
After studying a large collection of these forms, I am satisfied that they are va¬ 
rieties of the same species, dependent on age and the conditions surrounding them 
during their existence. 
PLATE CIV. 
Fig. 1 a. The dorsal side of a young specimen, where the length little exceeds the width ; 
the shell nearly all exfoliated. 
Fig. 1 b, c. Ventral and profile view of the cast of a larger individual, preserving a little 
of the shell. 
Fig. 1 d. Cardinal view of a cast of a specimen of medium size, which is more ventricose 
than 1 b, c. 
Fig. 2 a, b. Dorsal and profile of a large specimen of elliptical form, preserving a part of 
the shell in front. This is much less gibbous than usual in specimens of the same 
size. 
Fig. 3 a. Cardinal view of a large cast, the ventral valve uppermost. 
Fig. 3 b. Dorsal view of an individual of ovate form, preserving the greater part of the shell. 
Fig. 3 c. Cardinal view of a gibbous specimen. 
Fig. 3 d. Cardinal view of an extremely gibbous specimen, which is flat or slightly concave 
at the sides, and the centre of the ventral valve strongly elevated. 
Fig. 4. A fragment of stone presenting the aspect of these fossils in their usual condition in 
the rock. 
PLATE CV. 
Fig. 1. Dorsal valve of a full-grown individual, showing the abrupt inflection at the sides. 
Fig. 2. Profile of a large shell in which the parts are pretty well preserved in all their 
proportions ; the dorsal valve being partially exfoliated, and the striae not visible. 
Fig. 3. Yentral view of the preceding. 
Fig. 4. Dorsal view of a large specimen, which is unusually contracted at the sides on the 
lower half of the shell. 
Fig. 5. A partial cast of a ventral valve, showing the form of the muscular impressions and 
rostral cavity. The forms of the dental plates and teeth are seen on each side, 
below the beak. 
Fig. 6. A partial cast of a dorsal valve, showing a process reaching from the beak to the 
muscular impressions below. This process is the filling of the foramen, and ex¬ 
tends from the cavity of the dorsal valve beneath the bases of the crural supports, 
coming out at the apex of the beak. 
Geological position and localities. In the Oriskany sandstone : Albany, Greene, 
Ulster, Schoharie, Otsego, Herkimer, Cayuga counties, and at nearly all localities 
of the Oriskany sandstone in New-York; in Canada East and West, and in Penn¬ 
sylvania, Maryland and Virginia. 
[ Palaeontology III.] 
58 
