ARNOLD — THE PALEONTOLOdY AND STKATIGUAPHY OF SAN PEDRO. 195 



155. Helix (Epiphragmophora) sp. indet. 



Shell small, flattened, ylobosely conoidal; spire only slightly elevated; whorls three or four, 

 slightly convex; umbilicus narrow, deep; peristome expanded, nearly circular. 



An imperfect specimen of this genus was foiintl in tlie lower San Pedro series 

 and sent to Dr. Dall, who pronounced it a member of the above genus. 

 Living. — (?) 

 Pkistocene. — San Pedro (Arnold). 



Superfamily HYGROPHILA. 



Fiuniiy XJAa. LlMNiEID^E. 



Subfamily PLANORBIN^. 



Genus Planorbis Guettard. 



Shell discoidal, biconcave, the whorls visible on both sides; aperture small, roimded; 

 margin usually simple, sometimes expanded. 



Planorbis corneus Linne is a characteristic species. 

 156. Planorbis tumidus Pfeiffer. 



Plate IX, Fio. 1.3. 



Planorbis tumidus Pfeiff., Proc. Zool. Soc, 1861, p. 232. CpR., Brit. Assn. Rept., 1863, p. 558. 



Shell small, discoidal; spire, except last one and three-fourths whorls, slightly depressed; 

 whorls four, breadth and height about equal; suture deeply impressed, the whorls sloping toward it; 

 base cup-shaped, exhibiting all of the whorls; aperture exhibiting a slightly oblique section of a 

 somewhat angular cylinder; lip embracing over half of body-whorl and joined by callus. 



Dimensions. — Alt. 5 mm.; maximum diam. 12 mm. 



Distinguishable from P. vermicularis by less sloping upper side of body-whorl, 

 less depressed spire, and lip that is not expanded. Specimens identifled by Dr. Dall. 



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

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

 in the cuUection of Delos Arnold. 



Living.- — Guatemala (Carpenter) . 



Pleistocene. — San Pedro (Arnold). 



157. Planorbis vermicularis Gould. 



Plate IX, Fig. 14. 



Planorbis vermicularis Gld., Proc. Bost. Soc. Nat. Hist., Vol. II, 1847, p. 212; Wilkes' Expl. 

 Exped., Vol. XII, p. 112, fig. 131, 1852. Cpr., Brit. Assn. Rept., 1863, p. 675. 



Shell small, dome-shaped; spire sunken into cup shaped depression below upper margin of 

 body-whorl; whorls four, breadth and height about equal, the last one deflected near the aperture, 



