VALVATA.—COCHLIOPA. 427 
Depressed, subglobose, transversely wrinkled (or with slightly raised lines); spire convex, not prominent ; 
_ whorls 33, with the shoulder depressed (subsutural flattening) and an obtuse basal carina (Pilsbry) ; 
umbilicus rather large. Diam. less than + of an inch (under 5 millim.). 
Hab. Centrat Mexico: lakes around the city of Mexico (Heilprin 4). 
Var. pilsbryi, n. 
Valvata humeralis (Say), Pilsbry, loc. cit. p. 326 (specimens from Lake Patzcuaro) °. 
Whorls more rapidly increasing, without subsutural flattening, umbilicus narrower. 
Hab. Centra Mexico: Lake Patzcuaro (Heilprin®). 
Var. strebeli. . 
Valvata humeralis (Say), Strebel, Beitr. Mex. Land- und Siissw.-Conch. i. p. 33, t. 4. fig. 42 
(shell and operculum) (1878) ’. 
Valvata strebeli, Fisch. & Crosse, Miss. Scient. Mex., Mollusca, ii. p. 304 (1891) *. 
Depressed-conoidal, with wide umbilicus, and fine, closely set, raised strie across the whorls, greenish-horn- 
coloured ; whorls 33-32, rounded, without spiral keel. Diam. maj. 5, min. 4, alt. 4 millim.; aperture 
23 millim. in diameter, and 24-26 high. 
Hab. Centra Mexico: City of Mexico, in company with Planorbis tenuis, Limneca 
attenuata, and Physa osculans (Strebel? 8). 
It is much to be regretted that Pilsbry did not give a figure or the exact measure- 
ments of V. humeralis, of which he had typical specimens, as well as others collected 
by Prof. Heilprin, before him. Fischer and Crosse, it is true, give fairly good characters 
to distinguish V. humeralis from V. strebeli; nevertheless the two forms are very 
probably varieties of one species. The following points should be noted: (1) the 
similarity of the sculpture; (2) the known variability of the elevation of the spire in 
the European V. piscinalis ; (3) the fact that H. Pilsbry himself unites with V. humeralis 
the specimens from Lake Patzcuaro which want the subsutural flattening; (4) it is not 
very probable that of two nearly allied species living in the vicinity of the city of 
Mexico, Strebel should have found only the one and the two North-American travellers, 
Say and Heilprin, only the other. 
For Valvata guatemalensis, Morel., see the genus Cochliopa. 
COCHLIOPA. 
Cochliopa, Stimpson, Amer. Journ. of Conch. i. p. 52 (1865) ; Researches upon the Hydrobiine 
(Smithsonian Mise. Coll. no. 201), p. 50 (1865). 
Shell short-conoidal, solid, umbilicated, with fine spiral sculpture, and angulated at 
the base, greenish or olivaceous-brown without ; aperture very oblique, ovate, angulated 
above, the columellar margin somewhat dilated and expanded. Operculum thin, 
corneous, subspiral. ‘Tentacles rather long, tapering. 
The shell resembles in many respects that of Valvata, but may be distinguished 
54* 
