1920.] NATURAL SCIENCES OF PHILADELPHIA. 9 



development of small accessoiy cusps in the American species there 

 is no material difference. No North American genus has similar 

 teeth. 



Uncancylus ameliae n. sp. Fig. 4, left and lower figures. 



Rio Zapote, at confluence with the Rio Reventazon, 3450 ft. 

 March 4, 1910. Type and paratypes, No. 105260, A. N. S. P. 



With a general resemblance to U. calverti, this species is smaller, 

 relatively wider and higher. The periphery is elliptical, bilaterally 

 symmetrical. Anterior and left slopes are convex, right slope con- 

 cave and very steep, posterior slope somewhat concave; the apex 

 recurved, hook-hke, and very close to the right side, at the posterior 

 sixth of the length. Isabella colored, without gloss. Sculpture of 

 fine, thread-like radial striae, which are a little larger and more 

 widely spaced in front. 



Length 4.8, width 3.4, alt. 1.6 mm. 



AMPULLARIID.^. 

 Ampullaria fiagellata Say. 



Rio del Canas north of Santa Cruz, Guanacaste, 150 ft. 



AMNICOLID^. 

 Amnicola tryoni Pils. 



Brook near Rio Reventazon. Juan Vinas, 2500 ft. Four miles 

 southwest of Cartago, 4500 ft. A very young specimen, probably 

 of this species, was found attached to a dragonfly exuvia (Palaem- 

 nema sp.) at the nearer waterfall, Juan Vinas, 3300 ft. This species 

 was originally described from Javali, in the Chontales district, 

 Nicaragua, at 1750 ft. 



UNIONIDiE. 

 Nephronaias tempisquensis n. sp. Fig. 6. 



Rio Tempisque, Filadelfia, Jan. 18, 1910, 50 ft. Type and para- 

 types (2 whole specimens and 4 valves), No. 105225, A. N. S. P. 



The shell is oblong, the length slightly exceeding twice the alt., 

 beaks at about the anterior third. The dorsal and ventral margins 

 are but weakly convex, the anterior end rounded, posterior end 

 obliquely subtruncate. The beaks are eroded, but little projecting. 

 Surface somewhat glossy, under the lens showing very fine, hair-like 

 and somewhat wav^ed threads in the direction of growth lines, more 

 prominent on the posterior end. Color deep colonial buff with 

 numerous green rays. Interior white. The cardinal teetl^ are 

 compressed, in the left valve subequal, strongly crenulated, the 



