MOLLUSCA. 655 
this view, M. pygmeus being more attenuated and ascending in its fore end, more 
rounded and blunt in its hinder extremity. Hupé, in Castelnau’s work (quoted above, 
p- 540), figures both species. ‘The differences are well shown, and are corroborated by 
the specimens in the Berlin Museum; shells collected at Putumayo, Ecuador, by 
Hopke and Diibrich, pertaining evidently to VM. weddelli, help to fill the gap in the 
geographical distribution between Nicaragua and Chiquitos. 
PISIDIUM (p. 554). 
3. Pisidium compressum. 
Pisidium compressum, Prime, Proc. Bost. Soc. Nat. Hist. iv. p. 164 (1851) *; Monogr. Am. Corbi- 
culade, p. 64, fig. 67°; A. Gould, Rep. Invertebr. Massach. ed. 2, p- 110, fig. 419 (same 
figure) *; Dall, Proc. U.S. Nat. Mus. xix. p. 370 (1896) ‘. 
Very unequilateral and high, with a wing-shaped appendix on the summits. 
Long. 4, alt. 33, diam. 2} millim. 
Hab. N. Centrat Mexico: Lake Palomas, Mimbres Valley (Mearns). 
Widely distributed in North America, from Canada and New England to Ohio and 
Arizona1~+, Analogue of the European P. supinum, A. Schmidt. 
EXPLANATION OF PLATES. 
| [All figures are natural size, unless otherwise stated, the enlargement being indicated by the figures 
at the end of each line, thus 3 (one and a half times), &c. Plates 1-XV. were drawn by 
E. Duval, and the others by Fr. H. v. Zglinicka, both of Berlin ; II.-XV. were lithographed 
in England, the rest in Berlin; IX XVIII. only are coloured.] 
PLATE I. 
Cyclotus dysoni, Pfr., var. affinis, n. (p. 4), Bugaba, from three sides. . 
, specimen of smaller size, from San Isidro (p. 4), from three sides. 
Choanopoma rigidulum, Morel. (p. 16), Vera Paz, from two sides, t 
Chondropoma andrewse, Ancey (p. 16), Honduras, specimen received from M. Ancey, 
from two sides, $. 
subangulatum, nu. (p. 17), Teleman, from two sides, 3. 
Helicina succincta, n. (p. 86), Cordova, from three sides, $. 
—— deppeana, v. Mart. (p. 32): a, 6, two typical specimens, dorsal view. 
var., from Yalalag (p. 32), from three sides, and sculpture of the surface, 4. 
ek. var. (p. 36), Misantla: a, 6, two specimens, c, a young one, and 
Fig. 
eb 
—_— 
CHNAG 
sculpture, §. 
