PACHYCHILUS. 447 
Var. pyrgiscus. (Tab. XXV. fig. 6.) 
Melanoides obeliscus, Tristram, P. Z. 8. 1863, p- 418 *. 
Melania obeliscus, var. B, Brot, loc. cit. p. 24°. 
Pachychilus obeliscus, var. B. pyrgiscus, Fisch. & Crosse, loc. cit. p. 358, t. 50. figg. 9 a, 6°. 
Prominent portion of the whorls broken up into more numerous (about twelve) smaller knobs ; spiral ridges on 
the last whorl also well developed. Two specimens collected by the late O. Salvin are remarbably larger 
in size than those mentioned by Fischer and Crosse, viz.: long. 69, diam. 27; apert. long. 23, diam. 
14-15 millim. 
Hab. N. Guatemata: Lake of Peten (Salvin 4). 
Fischer and Crosse give no definite locality for this variety. 
Var. exarmatus, 
Melania obeliscus, var. y, Brot, loc. cit. p- 24, t. 3. fig. 157. 
Pachychilus obeliscus, var. y. exarmata, Fisch. & Crosse, loc. cit. p. 358°. 
Prominent portion of the last two whorls without knobs; spiral ridges strongly developed. 
Hab. t Honpuras. 
The habitat of this form is not expressly stated. According to Brot, the varieties 
are connected by intermediate examples. 
8. Pachychilus lacustris. 
Melania lacustris, Morelet, Test. Noviss. i. p. 25 (1849)'; Brot, in Martini & Chemnitz, Syst. 
Conch.-Cab. ed. 2, Melaniaceen, p. 25 ’. 
Pachychilus lacustris (Morelet), Fisch. & Crosse, Miss. Scient. Mex., Moll. ii. pp. 358-362 °. 
Fischer and Crosse are right in observing that P. lacustris torms a polymorphous 
series analogous to that of P. glaphyrus; but I think P. odeliscus ought also to be 
included, the P. lacustris varr. amphibolus and terebralis of those authors being indeed 
not separable from P. obeliscus. 
a. lacustris, 8. str. 
Pachychilus lacustris (Morelet), Fisch. & Crosse, loc. cit. p. 359, t. 52. figg. 4, 4a, and t. 51. 
figg. 3,3a*. 
Vertical plaits and spiral ridges developed. Shell moderate in size. Long. 39-52, diam. 16-183 ; apert. long. 
13-17 millim. 
Hab. EF. Guatemata: lake near the town of Yzabal (Morelet}?); Lake of Yzabal 
(Bocourt?*); Panzos (Conradt, in Mus. Berol.). 
b. Var. amphibolus. (Tab. XXV. fig. 7.) 
Pachychilus lacustris, var. t. amphibola, Fisch. & Crosse, loc. cit. p. 360, t. 52. fig. 3°. 
Vertical plaits rather feeble ; one of the spiral ridges more prominent, forming a knobbed keel on the last 
two whorls somewhat beneath the sutural line. 
Long. 62, diam. 21; apert. long. 18 millim. Whorls 9 (Fisch. & Crosse). 
60, » 23; ” 21 Whorls 8 (specim. Stoll). 
7 
