THE NAUTILUS. 51 



The type of this group was at first taken for a Planorbis of the 

 P. dilatalus group, 1 but when the dentition was examined it became 

 obvious at once that the snail could not belong to the Planorbinse. 

 The radula is not materially unlike that of Amphigyra, but the con- 

 chological features of the two groups are quite diverse, Amphigyra 

 being Crepiduloid with a distinct " deck " or columellar plate, while 

 Neoplanorbis is Planorbis-shaped, perforate, with a carinate periphery 

 and no " deck." 

 Neoplanorbis tantillus n. sp. PI. Ill, figs. 3, 4, 5. 



Shell very narrowly perforate, slightly convex above, very con- 

 vex below, with a strongly projecting rounded keel at the periphery ; 

 light brown; surface slightly shining, sculptured with very obliquely 

 radial growth-lines and raised spiral striae, rather coarse for a shell 

 of this size. Whorls 2, rapidly enlarging, the apex somewhat 

 sunken; first whorl very convex, the second much less so, slowly 

 descending in front. Aperture very oblique, shaped like a gothic- 

 arched door, the upper and lower margins arcuate, the outer margin 

 angular, the columellar margin dilated, straight and vertical, with a 

 rather wide whitish callous within. Alt. .8, diam. 1.7 mm. 



The specimens occurred at Wetumpka, Alabama with the preced- 

 ing species. This is one of the smallest fresh-water mollusks yet 

 found in America. 



NOTE ON LEPYEIUM, 



BY H. A. PIL9BRY. 



In connection with the genus Amphigyra I have had occasion to 

 examine the specimens of Lepyrium in the collection of the Academy. 

 It appears that the Lepyrium from the Cahawba river differs from 

 L. showalteri (Neritina shoivalteri Lea) of the Coosa, in being much 

 smaller, alt. 2.7, diam. 3 mm., with a straighter columellar edge and 

 without a raised outer margin of the columellar area. It will prob- 

 ably prove specifically distinct, but as I have been able to compare 

 only one of the original lot of L. showalteri, it may be best to rank 

 the Cahawba form at a subspecies under the name Lepyrium showal- 

 teri cahawbensis. 



1 It was reported a9 Planorbis tantillus in Mr. Hinkley's list, Nautilus XVIII, 

 p. 64. 



