456 | MOLLUSCA. 
especially in the affluents of the Rio Usumacinta; but as his specimens have not been 
seen by me, I can neither confirm nor refute his statement. 
Var. costato-plicatus. | 
Pachychilus levissimus (Sow.), Tristram, P. Z. 8. 1863, p. 413”. 
Melania levissima, var. a. costato-plicata, Brot, loc. cit. p. 35, t. 5. fig. 5". 
Pachychilus levissimus, var. y. costatoplicatus, Fisch. & Crosse, loc. cit. p. 829, t. 33. fig. 5, 
With numerous more or less distinct vertical plaits. 
Hab. S.E. Mexico: Palenque, with the type-form (Morelet ° *). 
N. Guatemana: Rio de la Pasion, Alta Vera Paz (Salvin '”). 
Var. varicosus. 
Melania corvina, var. «, Brot, loc. cit. p. 37, t. 5. figg. 1, la », 
Pachychilus levissimus, var. 8. varicosa, Fisch. & Crosse, loc. cit. p. 329, t. 58. fig. 6 °°. 
With several strong vertical plaits, transversely ridged. 
Hab. SE. Mexico, Palenque (Morelet }° '°). 
Having examined a large number of Venezuelan specimens of P. levissimus, Sow., I 
cannot follow Brot and Fischer and Crosse in regarding it as identical with P. indiorum, 
Morel., of E. and S.E. Mexico. The Venezuelan shell is thicker and ovoid ; the upper 
whorls are only a little more convex, the spire in consequence not being so exactly 
conical in P. levissimus, but rather convex-conical (very often, however, it is much 
eroded) ; the last whorl, on the contrary, is more convex in its greatest periphery in 
P. indiorum, more oblong and compressed in P. levissimus; the peristome in this 
latter is very thick and blunt, produced below anteriorly in such a manner that the 
whole plane of the aperture becomes concave, protuberant beneath, and the junction 
of the basal with the columellar margin is rounded, not angular as in P. indiorum. 
M. helleri (Parr.), Brot, Matériaux fam. Mélaniens, iii. p. 29, t. 4. fig. 1 (1872); and 
in Martini and Chemnitz, Syst. Conch.-Cab. ed. 2, Melaniaceen, p. 33, t. 4. fige. 4a, d, 
appears to me to be identical with the Venezuelan form, and therefore with P. levissimus, 
Sowerby, Hanley (Conch. Miscell. t. 3. fig. 23), and Reeve (Conch. Icon. xii. fig. 126). 
The localities given by Parreyss for his exotic shells are often unreliable. 
M. radix, Brot, merely differs from P. indiorum in having a comparatively smaller 
aperture and a more swollen last whorl ; he gives as locality ‘‘ Central America.” 
Morelet wrote “indiorum ”: the classical name for the people of India is “ Indi,” 
gen. Indorum ; he did not, however, mean the inhabitants of the East Indies known 
to the classical writers, but the American natives, called “ Indios ” by the Spaniards ; 
we may therefore tolerate the form indiorum. 
11. Pachychilus dalli. (Tab. XXVI. fig. 4.) 
Pachycheilus dalli, Pilsbry, Science, new series, 111. p. 608 (April 1896); Proc. Acad. Phil. 1896 
p. 269, with fig. *. 
Pachycheilus walli (Pilsbry), Zool. Anzeiger, xix. no. 502, p. 228 (1896) (typographical error) ® 
