130 PALAEONTOLOGY OF CALIFORNIA. 



single cast, will probably be found to belong 

 to the subgenus Luponia. From the narrow- 

 ness of the aperture, the shell appears to have 

 been thin. The accompanying outlines illus- 

 trate the form better than would be possible in 

 a description. 



POTAMIDES, Brongn. 



P. DIADEMA, 11. S. 

 PL 20, Fig. 85. 



Shell turriculated ; spire high; whorls eight, concave, and 

 sloping above, carinate, and strongly undulated on the angle by 

 sharp, flattened tubercles; suture impressed, linear. Surface 

 marked by numerous, fine, somewhat irregular, revolving lines, 

 larger below the carina, and by tine lines of growth. Aperture 

 broad above, rapidly narrowing below. Outer lip acute, retreat- 

 ing from the suture to the carina, sinuous below. Columella 

 lightly iucrusted. Canal short, nearly straight, not emarginate 

 in front. 



Figure, natural size. 



Locality: Abundant on the north fork of Cottonwood Creek. (Div. A.) 



P. TENUIS, 11. S. 

 PL 20, Fig. 80. 



Shell elongated, slender ; spire high ; whorls increasing gra- 

 dually in size, seven to seven and a half. Upper two-thirds 

 sloping almost perpendicularly; lower third sloping rapidly 

 inwards towards the suture, which is narrowly channelled. 

 Angle of whorls marked by pretty distinct, elongated tubercles, 

 which, on the body whorl, sometimes take the form of elongated 

 sinuous ribs; at other times the surface of this whorl is smooth. 

 Aperture elongated, acute behind, widest in the middle, con- 



