196 CALIFORNIA ACADEMY OF SCIENCES. 



rounded at periphery; suture very deep, the whorls sloping toward it; base cup-shaped, exhibiting 

 all of the whorls; aperture exhibiting a very oblique section of a cylinder; slightly expanded, em- 

 bracing about one-half the height of the last whorl, and joined by callus. 

 Dimensions. — Alt. 6 mm.; maximum diam. 11.5 mm. 



Specimens identified by Dr. Dall. 



Rare in tlie upper and lower San Pedro series at San Pedro; three specimens. 

 The specimen figured is from the upper San Pedro series at San Pedro, and is now 

 in the collection of Delos Arnold. 



Living. — Interior of Oregon (Gould). 



Pleistocene. — San Pedro (Arnold). 



Family XLVII. PHYSID/E. 

 Genus Physa Draparnaud. 

 Shell ovate, sinistrally spiral, thin, polished; aperture rounded in front. 

 Physa foniinalis Linn, is a characteristic species. 



158. Physa heterostropha Say. 



P/iysa /le/erosirop/ia Sav, Nichohon's Encych, PI. LXIX, fig. 6. Cpr., Brit. Assn. Rept., 1863, 

 p. 674. Keep, West Coast Shells, p. 118, fig. 107, 1892. 



Shell small, sinistral, shining, pellucid; whorls five ventricose; suture distinct; aperture 

 oval; outer lip thin; pillar lip strong and forms a con.spicuous sinus where it joins the whorl above. 



Dimensions. — Long. 12 mm.; lat. 7 mm.; body-whorl 10 mm.; aperture 8 mm.; defl. 

 95 degrees. 



This fresh-water form, together with several other s^iecies having the same 

 hiihitat, was found in the lower San Pedro beds at San Pedro. There is no doubt as 

 to their occurrence in these marine deposits, into which they were probably washed 

 by some fresh-water stream. 



Living. — North America. 

 Pleiatocene. — San Pedro (Arnold). 



Superfamily DITREMATA. 

 Family XLVIII. AURICULID/E. 



Subfuiniiy MELAMI'INjE. 



Genus Melampus Montfort. 



Shell oval-conoidal, or suboval, solid; spire rather .short; aperture elongated, narrow; 

 coliimellar lip with several dentiform ])licalions; columella plicate; outer liji sliarp, interior wiili 

 revolving ridges. 



Melampus luieus Quoy is a characteristic species. 



