ARNOLD— THE PALEONTOLOGY AND STKATIORAPHY OF SAN PEDRO. 305 



338. Rissoa acutelirata Carpenter. 



Platk IV, Fui. 1-.'. 

 Rissoa acutelirata Cpr., Brit. Assn. Rept., 1863, p. 656. 



Shell minute, conical, pointed, rather thick; whorls five, convex, with fifteen sharp, distant, 

 spiral riblets, traveling over eighteen sharp distant ribs, which are obsolete on base of body-whorl; 

 aperture ovate; peristome entire, continuous. 



Dimensions. — Long. 1.5 mm. 



This minute little shell is seen under the microscope to have a very cancellated 

 sculpture. Specimens identified by Dr. Dall. 



Rare in upper San Pedro series of San Pedro. Two specimens. Found also 

 in the Pleistocene at the old irrigating ditch, Ventura. The specimen figured is 

 from the upper San Pedro series at San Pedro, and is now in the collection of 

 Delos Arnold. 



Living. — San Diego (Carpenter). 



Pleistocene. — San Pedro; Ventura (Arnold). 



Subfamily HYDROBIIN.^. 



Genus Paludestrina d'Orbigny. 



Shell conical, more or less elongated; smooth, imperforate or nearly so; ape.x acute; aperture 

 ovate; peritreme continuous; outer lip acute; inner lip not thickened. 



Paludestrina piscium d'Orbigny is a characteristic species. 

 339. Paludestrina curta, sp. uov. 



Pi,ATF. VIII, Fig. 2. 



Shell small, conical, very thin; spire elevated; apex rounded; whorls four, very convex, 

 smooth, except for obsolete transverse scul[)ture; suture deeply impressed, distinct; aperture oval; 

 peritreme continuous, thin; umbilicus subperforate. 



Dimensiom. — Long. 4 mm ; lat. 2.2 mm.; body-whorl 2.6 mm.; aperture 1.5 mm.; dctl. 

 38 degrees. 



Distinguishable from P. stokesi by much broader shell, fewer whorls, and more 

 perforate umbilicus. Pronounced a new species by Dr. Dall. 



Rare in lower and upper San Pedro series of San Pedro. The specimen 

 figured is the type, which is from the lower San Pedro series at San Pedro, and is 

 now in the United States National Museum. 



Pleistocene. — San Pedro (Arnold). 



340. Paludestrina stokesi, sp. nov. 



Plate VIII, Fici. .1. 



Shell small, conical, thin; spire elevated; apex acute; whorls six, very convex; surface with 

 faint, nearly obsolete, rounded, transverse ridges; suture deeply impressed, distinct; body-whorl 



( 39 ) April 27, 1903. 



