PACHYCHILUS. 463 
Hab. Centra Mexico: in swamps in the woods bordering the Rio Grande, between 
‘‘’Tampico and Mexico” (Saussure 1-3), 
This river, which must not be confused with the well-known Rio Grande del Norte, 
runs into the Lagoon of Meztitlan, the road from Tampico to Mexico city crossing it 
between Zacualtipan and Atotonilco, in the State of Hidalgo. The Lagoon of Meztitlan 
lies west of the Sierra Madre and does not drain into either the Atlantic or the 
Pacific *. 
D. Subgen. PoTaMaNax. 
Potamanaz, Pilsbry, Proc. Acad. Phil. 1892, p. 341. 
Shell short, ventricose, approaching to the ovate form; aperture simply rounded 
beneath, with thickened, callous, columellar margin. 
21. Pachychilus sargi. 
Melania sargi, Crosse & Fisch. Journ. de Conch. xxiii. p. 226 (1875) *; xxiv. t. 11. fig. 4°; Brot, 
in Martini & Chemnitz, Syst. Conch.-Cab. ed. 2, Melaniaceen, p. 333, t. 34. figg. 12, 12 a’. 
Pachychilus sargi, Fisch. & Crosse, Miss. Scient. Mex., Moll. 1. p. 338, t. 51. figg. 6, 6a, 7°. 
The shortest and most Littorzna-like of all the Central-American species. Last whorl subangulated. 
Hab. N. Guatemata: Coban (Schneider *) ; Cahabon (Champion). 
The typical specimens were found by Mr. Sarg, probably in the vicinity of Coban, 
where he resided fora long time. Crosse and Fischer merely give “ Guatemala (Sarg) ” 
as the locality 12. 
22. Pachychilus pilsbryi, n. x. 
Potamanaz rovirosai, Pilsbry, Proc. Acad. Phil. 1892, p. 341, t. 14. figg. 8,9°. 
Very near the preceding, but with the last whorl simply convex, not subangulated, and with more distinct 
spiral lines. 
Hab. S.E. Mexico: mountains of Poana, State of Tabasco (Lovirosa *). 
As there is a Pachychilus glaphyrus, var. rovirosai, mentioned on a preceding page 
in Pilsbry’s paper (Joc. cit. p. 339), the name of the present species must be changed. 
Pilsbry says that the operculum of his genus Potamanax is very different from 
that of Pachychilus, it having but few whorls, with a basal nucleus; but as the 
operculum of the two Central-American species of this section is nat yet knowa, 
Pilsbry’s description of it having been taken from the Cuban P. drevis, d'Orb., which 
he treats as congeneric, I prefer to keep the two Central-American forms in the genus 
Pachychilus until further information is obtained. 
* T am indebted to Dr. Seler, of Berlin, for information as to the position of this river, which is not marked 
on most maps. 
