160 MOLLUSCA. 
31. Helix sigmoides. 
Helix sigmoides, Morelet, Test. Noviss. 11. p. 9 (1851) +; Pfr. Monogr. Helic. Vivent. lil. p. 737. 
Helix (Gonostoma) sigmoides, Fisch. & Crosse, Miss. Scient. Mex., Mollusca, i. p. 239, t. 12. figg. 6, 
6 a-d°?; Journ. de Conch. xxi. p. 275 (1878) *. . 
Helix (Odontura) sigmoides, Strebel, Mex. Land- und Siissw.-Conch. iv. p. 38’. 
Helix vitrinoides, Tristram, P. Z. S. 1863, p. 411° (nec Deshayes). 
Zonites vitrinoides, Fisch. & Crosse, Miss. Scient. Mex., Mollusca, i. p. 1707. 
Hab. N. Guatemata: woods of the province of Vera Paz, in holes covered by dense 
bush, rare (Morelet }~°, and in MS.) ; forests of Vera Paz (Salvin ®"). 
Owing to the kindness of M. A. Morelet and of the Rev. H. B. Tristram I have been 
able to compare typical specimens of Helix sigmoides and H. vitrinoides, and find that 
they agree both in form and sculpture, the latter only a little more worn in H. vitrinoides. 
The sculpture appears, under a moderate magnifying-power, as if formed by small 
granules, disposed in quincunx, the more distinct rows of which are not parallel to the 
aperture, but descend from above and before to below and behind. Viewed under a 
stronger lens each granulum proves to be crowned by a little hole or dimple, in the 
midst of which a small eminence is situated ; probably each is the scar of ahair. This 
sculpture extends in equal intensity on the lower side of the shell to the brim of the 
umbilicus. 
The thin simple edge of the aperture and the small number of the whorls (‘Tristram ° 
mentions 44—in his specimen I can see only 3$) induced Strebel to suggest that 
H. sigmoides might be a young shell; but this is somewhat contradicted by the fact 
that the line of the suture is distinctly bent down near the aperture, as in full-grown 
shells: Morelet found several specimens of equal size at the same spot, and he is under 
the impression that they are full-grown. Fischer and Crosse ® place it in the sub- 
genus Gonostoma, which contains European species with many narrow whorls. Strebel 
compares it with young specimens of Helix ghiesbreghti; but in this species the lower 
face of the shell is smooth. The sculpture much resembles that of Solaropsis, some 
smaller species of which have also a thin, nearly straight, edge of the aperture, and a 
flat or even concave spire. I place the species provisionally in Solaropsis. 
Doubtful species of Helix. 
The following species have been described by trustworthy authors as belonging to 
the Mexican or Central-American fauna; but they have not again been found by later 
collectors :— . 
Helix mexicana. 
Heliz mewxicana, Fr. Koch, in Philippi’s Abbild. neuer Conch. i. p. 28 .(7), t.2. fig. 5 (1843) *; 
Pfr. Symb. Hist. Helic. ii. p. 83°; Monogr. Helic. Vivent. i. p- 193°; in Martini & 
Chemnitz, Syst. Conch.-Cab. ed. 2, Heliz, ii. p. 153. no. 591, t. 93. figg. 1, 2°. 
Helix (Leptawis) mexicana (Fr. Koch), Fisch. & Crosse, Miss. Scient. Mex., Mollusca, i. p. 238°. 
