PACHYCHILUS. 449 
Morelet! remarks of this species: “ MW. lacustris circa pagum Yzabal,” which leaves 
it uncertain whether his. specimens were from the great lake only or from other waters 
near it. Fischer and Crosse ® give no special indications of localities for their different 
varieties, but merely say generally: ‘Le type et les variétés proviennent du lac Yzabal 
et des cours d’eau voisins” (loc. cit. p. 862). Herr Conradt has given to the Berlin 
Museum the following forms from Panzos:—Jacustris, sens. strict.; var. conradti; a 
specimen intermediate between the varr. major and elimatus; and, finally, the var. 
pumilus. Panzos is situated in the valley of the Polochic river, which drains into the 
Lake of Yzabal. All his specimens are of a shining black colour. 
Brot’s var. 8, t. 3. fig. 26,— Fischer and Crosse’s var. y. eatenuata, is rather an 
imperfect much-worn specimen than a distinct variety. 
4. Pachychilus pluristriatus. (Tab. XXVI. fig. 1.) 
Melania pluristriata, Say, in New Harmony Disseminator of Useful Knowledge, Dec. 1831°; 
Complete Writings, p. 140°; Brot, in Martini & Chemnitz, Syst. Conch.-Cab., ed. 2, 
Melaniaceen, p. 44’. 
Pachychilus pluristriatus, Fisch. & Crosse, Miss. Scient. Mex., Moll. i. p. 370%. 
Melania rubida, Lea, Proc. Acad. Phil. 1856, p. 145°; Obs. Unionide, xi. p. 77, t. 22. fig. 16 
(1864) °; Brot, loc. cit. p. 341, t. 34. fig. 27 (copy from Lea). 
Pachychilus rubidus, Fisch. & Crosse, loc. cit. p. 371 °. 
Melania labiosa, Wiegmann, in Mus. Berol.’. 
Conico-turrite, encircled with elevated, sharply defined, spiral ridges, of which six are visible on the penultimate 
whorl, five on the upper half of the last whorl, and 8-10 less distinct ones on the basal half of the latter ; 
the ridges are not exactly equal—in one specimen, for instance, the second and fifth on the penultimate 
whorl are distinctly more feeble, in another the third is stronger than the rest; on the upper whorls the 
fourth is usually the most prominent. Preserved whoris eight, probably one or two only lost, almost 
even, apart from the prominent ridges, the sutures shallow ; the last whorl divided from the preceding 
by a very deep suture and also more rounded, very convex below. The aperture occupies rather more 
than a third of the whole length of the shell; it is ovate, rounded above and distinctly produced below ; 
the outer margin is simple, rounded ; the columellar margin is much thickened, smooth, and glossy. The 
specimens before me from the Laguna of Chapala are quite bleached, whitish; Say gives the colour as 
reddish (rufescens), and according to Lea it is rusty (ferruginea). 
. Long. 35, diam. 13; apert. long. 13, diam. 93 millim. 
a 
b. a) 26, 29 12 3 ” 11, ” 8 ” 
C. 39 33, ” 13 3 2 13, oP) 10 9 
a «6 6S1, 14. 
a, 6. Dimensions of the specimens in the Berlin Museum ; ¢, as shown in Lea’s figure; d, as given by Say 
(12 and 4) inch). 
Hab. Centrat Mexico: Laguna de Chapala, in the district of Guadalajara, western 
part of the Mexican plateau (Deppe®); Mexico, without nearer indication of 
locality (Say1~?); Mexico, probably from the central plateau (Hon. J. R, 
Poinsett °°). 
This is the only known species of Melaniide which is peculiar to the tableland of 
Mexico, and I am even not sure whether it is still living or extinct: Deppe’s specimen 
BIOL. CENTR.-AMER., Terr. and Fluviat. Mollusca, Movember 1899. 547 
