562 PROCEEDINGS OF THE ACADEMY OF [1896. 



narrow on the left side, the periphery very obtusely angular near 

 the left side. Aperture quite oblique, cordate, the peristome thin 

 and fragile, produced forward on the right side. 



Alt. r7, diam. 7 mm. 



Ponds and small streams near Maid on ado, Uruguay (Dr. Rush !). 



Compared with P. heloicus d'Orb., this species is flatter and more 

 glossy, has the spire much narrower on the right side, the outer 

 whorl wider and less cylindrical ; the color is darker and the 

 periphery rounded-angular. 



Planorbis heteropleurus Pilsbry & Vanatta, n. sp. PI. XXVI, iags. 1, 2, 3. 



Shell moderately solid, corneous-white, rather opaque, the surface 

 with fine, close growth-lines ; earlier whorls rather deeply and 

 about equally sunken on the two sides ; convex, and strongly angu- 

 lar or keeled in the middle, on the right side ; periphery conspicu- 

 ously carinated on the left side, which is shallowly vortex-shaped, 

 the whorls nearly flat. Last whorl slightly wider on the right than 

 on the left side. Whorls 3 J, all visible on both sides, the last wider 

 than the spire. Aperture very oblique, rounded-pentagonal, the 

 right margin produced forward. 



Alt. 4i, greatest diam. 11 J, lesser 8} mm. ; oblique alt. of aper- 

 ture 5J, diam. 4 mm. 



Lake Titicaca (A. Agassiz !). Types No. 69,645, collection of 

 the Academy of Natural Sciences of Philadelphia. 



This remarkable species is totally unlike P. titicacensis Cless.,' P, 

 montanus d'Orbigny^ and P. andicola d'Orbigny,^ species already 

 known from this Andean lake. It is most like P. andicola, but 

 much flatter with diflferently placed keels, and, in fact, so diverse in 

 characters that no profitable comparison can be made. Described 

 from eight specimens, which are alike in all essential characters. 



CYRENID^. 



Corbicula Coloniensis n. sp. PI. XXVI, fig. 9. 



Shell subtriangular, rather ventricose, slightly inequilateral ; an- 

 terior and posterior margins obtusely angular, the slope above the 

 rounded angles slightly convex ; posterior slope decidedly longer ; 

 basal margin well curved, rounded ; beaks moderately projecting. 

 Hinge ligament very convex, short and yellowish. Surface nearly 



^ Conchylien Cabinet, Planorbis, p. 147, pi. 1 2, f. 23-25. Clessin locates 

 Lake Titicaca in Ecuador I On p. 175 lie calls the species P. titicacaensis. 

 "■ Voy. Am. Merid., p. 345, pi. 44, f. 5-8. 

 Ubid.,^. 346, f. 1-4. 



