Subfamilies, Genera, and Subgenera — Recent and Fossil 191 



narrowly iinibilicatc, but it has a spire of closely coiled whorls like 

 Drepanotrema. The small size and umbilicate left side are like Menetus, 

 which, as Arnold thought, is probably its nearest relative; but in carinate 

 species of Menetus the keel is peripheral' (Pilsbry, 1934, p. 568). 



'The shell of the type species, Planorbifex vanvlecki, varies in the 

 amount of flattening of the base; sometimes it is scarcely noticeable. The 

 species was referred by Dr. Cooper to Valvata virens, a very different shell. 

 It has certain resemblances to such forms as Valvata bicarinata Lea, but 

 the excised outline of the strongly oblique aperture, and the thickened 

 peristome, exclude a reference to the Valvatidae, some of which have a 

 similar sculpture' (Pilsbry, 1934, p. 569). 



As remarked under the genus Paraplanorbis, it appears better to regard 

 Planorbifex as a separate genus related to Menetus rather than as a sub- 

 genus of Menetus. The carina in the middle of the whorl of the right side 

 is distinctive, and is different from any known species of Menetus or Pro- 

 menetus, where the carina is peripheral or just below the margin of the 

 left side. 



