50G GEOLOGY OP THE YELLOWSTONE NATIONAL PARK. 



Pleurotomaria (?) sp. 



A rather large gastropod shell, broken and embedded in limestone. 

 Height, about 22.5 mm.; diameter at base, 25 mm.; whorls, five or six. 

 Umbilicus extending through three or four whorls. Apparently without 

 ornamentation. Cross section of whorl subquadrate, the upper and lower 

 faces converging centripetally, the distal and proximal faces converging 

 toward the apex. Shell thick, interior section of whorl nearly circular. 



The matrix inclosing the specimen is weatherworn so as to form a 

 transverse section somewhat more than half through the shell. From this 

 the above notes were taken. The surface as represented by section is 

 unornamented, for the line representing the outer face is simple and entire. 

 Although a certain identification is impossible, this fact operates against 

 referring the form to Pleurotomaria. It may go with the genus Paleeo- 

 trochus, but is distinct from anything yet referred thereto. 



Formation and locality: Three Forks limestone, north side of saddle 

 west of Mount Miller, Absaroka Range; Louis V. Pirsson. 



LOXONEMA Phillips, 1841. 



LOXONEMA DELICATUM n. Sp. 

 PL LXVI, fig-. 6a. 



Shell very small, elongate. Spire consisting of about five volutions; 

 whorls well rounded and suture line depressed. Aperture nearly circular. 



The specimen described is a cast, not showing any surface characters. 

 It is found associated with Platystoma minutum and other gastropods (see 

 ante, p. 482). 



Formation and locality: Three Forks limestone, south side of Soda 

 Butte Creek, northeast of Abiathar Peak, Absaroka Range; J. P. Iddings. 



PLATYSTOMA Conrad, 1842. 



Platystoma minutum n. sp. 

 PI. LXVI, figs, 7a, lb. 



Shell extremely small, conical, flattened. Spire low and consisting of 

 about three volutions. Aperture somewhat oblique, elongate, elliptical. 

 Surface nearly smooth, ornamented, if at all, only with lines of growth. 



