ANCYLUS.—GUNDLACHIA. 403 
The two Costa Rican forms appear to be sufficiently distinct from one another to be 
Pegurded as distinct species; but the typical A. excentricus from Guatemala, according 
Fischer and Crosse’s description and figure, seems to be intermediate between them, 
in regard to the relation of the breadth to the length of the shell and to the position 
of the apex. | 
0bs.—A. culicoides, d’Orb. Mag. Zool. 1835, Classe V. no. 61, p.23; Voy. Am. mér., 
Moll. p. 355, t. 42. fige. 9-12, from Guayaquil, Ecuador, is very near A. excentricus : 
according to the figure, it appears to have a blunter summit to the shell. 
Dr. O. Stoll has also found some specimens of Ancylus in Central Guatemala, in 
small streams near the capital, and in West Guatemala, in wells at Retalhuleu; but as 
they are not available at the present moment for examination, it is impossible to 
identify them. 
GUNDLACHIA. 
Gundlachia, Pfeiffer, Zeitschr. f. Malak. 1849, p. 97; H. & A. Adams, Gen. Moll. ii. p. 267. 
Shell resembling that of Ancylus, but with the apex prolonged backwards into a 
cylindrical tube, exceeding considerably the hinder margin of the aperture, and the 
inside provided with a horizontal septum, like that of the marine genus Crepidula— 
comparatively very large in the young shell, more reduced in the full-grown one. 
Median tooth of the radula bicuspid; laterals multicuspid. 
Several species in the Antillean islands, one in California, one in Honduras, and one 
in Tasmania. 
1. Gundlachia hjalmarsoni. 
Gundlachia hjalmarsoni, Pfr. Malak. Blatt. v. p. 197 (1858) *. 
Oval-oblong, with fine radial lines, pale horn-coloured ; apex rounded ; the basal septum occupying 4 of the 
whole length, its anterior edge concavely arched, basal margin before and behind somewhat elevated. 
Length 4, diam. scarcely 2, height 13 millim. 
Hab. Honpuras: Santa Rosa (Hjalmarson, 1852-53 3). 
51* 
