152 MOLLUSCA. 
Europe ; sides broad, hinder end somewhat tapering. Length of the crest on the back 
of the foot behind the shell 2°83 centim. Feelers and face blackish; back blackish- 
grey, with a broad ochre-yellow line in the centre ; sides yellowish-grey ; crest white ; 
lateral edges and hinder end brownish-grey; the furrows between the warts deep 
brown. Sole greyish-white, white-dotted, with broad, somewhat darker lateral edges. 
Collar greyish-brown ; stalk of the trunk within the aperture milk-white. Face higher 
than broad, convex, steeply sloping. The crest on the back of the foot can be with- 
drawn so deeply, that it leaves a furrow instead of the prominence. If the animal is 
irritated, it jerks the shell from one side to the other in regular movements. It lives 
in lofty forests, and gradually becomes rarer near the settlements by the burning of the 
forests. In former times it was used as Lenten-food by the Indians of the department 
of Vera Paz, as also the Melanie.” 
Several of the above-named varieties may be scarcely more than individual variations : 
the whole underside is sometimes of the same dark brown colour as the lower band, or 
may be of an intermediate reddish-brown, sometimes very bright, or of the same pale 
fawn colour as the rest of the shell between the bands; the bands are dark brown, but 
some or all of them are occasionally paler, more reddish, or even quite obsolete. But 
these differences of colour are very striking, more especially in the var. strudelli; the 
var. rufo-zonata seems to be also geographically limited. 
The colour of the hairs, where they are preserved in the dry shells from Cerro Zunil, 
is a pale grey; in the var. strubelli they are black. 
The size of adult specimens varies from 63-77 millim. in diameter, rather indepen- 
dently of the coloration ; the elevation of the spire is also somewhat variable in com- 
parison to the diameter. I have before me two specimens of 69 and of 75 millim. in 
diameter, both equally 52 millim. in height. 
Subgen. Oxycuona, Morch. 
Oxychona, Mérch, Cat. Conch. Yoldi, i. p. 14 (1852) (type Helix bifasciata, Burrow). 
Geotrochus (b. Species brasilienses), v. Martens, in Albers’s Die Helic. ed. 2, p. 168. 
Geotrochus and Corasia, Fischer & Crosse, Miss. Scient. Mex., Mollusca, i. pp. 291, 296. 
Shell smooth and shining, whitish, with various dark spiral bands and sometimes 
dark spots, angulated or even keeled, more or less conical above, flat below; margins 
of the aperture rather thick and conspicuously expanded and reflexed. Back of the 
foot with a knobbed keel as in Odontura (at. least in H. trigonostoma). 
Although the anatomy is not yet known, I feel convinced that Helix trigonostoma, 
H. bicincta, H. guillarmodi, H. costaricensis, and H. adela form a natural group of 
Neotropical Helices, agreeing chiefly in the bright-coloured, shining, and nearly smooth 
surface of the shell, the angularity of the whorls, and the reflexed margins of the aper- 
ture. The differences between them consist chiefly in the degree of the angularity of 
