166 | MOLLUSCA. 
Var. tholus: major, umbilico latiore. 
Helix (Polygyra) tholus, Binney, Proc. Acad. Phil. ix. p. 186 (1857) °. 
Heliz tholus, Binney, Terr. air-breath, Moll. N. Am. iv. p. 81, t. 78. fig. 21"; Binney & Bland, 
loc. cit. p. 95, fig. 171"; Pfr. Monogr. Helic. Vivent. iv. p. 351”. 
Dedalochila tholus (Binn.), Tryon, Am. Journ. Conch. iii. pp. 64, 78, t. 3 (10). figg. 7, 9”. 
Heli« couloni, v. Mart. in Malak. Blatt. xii. p. 22 (1865) (nec Shuttl.)”. 
Hab. Norta America: Texas? 1°12; Washington County, Texas 1*. 
E. Mexico: Vera Cruz, one worn specimen, 10 millim. in diameter (Friedel '*). 
Recognizable by the convex upper side, and by the distinct spiral groove on the side 
of the penultimate whorl within the umbilicus, which is more or less wide, but always 
open, not obstructed. It varies much in size, the largest specimens (¢holus) measuring 
11 millim., the smallest, from Texas, scarcely 7 millim. The arrangement of the teeth 
is essentially the same as in P. terasiana. 
6. Polygyra yucatanea. 
Helix yucatanea, Morelet, Test. Noviss. i. p. 9 (1849)*; Pfr. Monogr. Helie. Vivent. iii. p. 2637; 
Folin, Journ. de Conch. xiii. p. 68 (1865) (living animal, eggs) °. 
Helix (Polygyra) yucatanea (Morel.), Fisch. & Crosse, Miss. Scient. Mex., Mollusca, i. p. 277, t. 12. 
figg. 14, l4a’*. 
Triodopsis yucatanea (Morel.), Tryon, Am. Journ. Conch. iii. p. 52, t. 4 (9). fig. 17 (very bad) 
(1867) °. 
Hab. 8.E, Mexico: Tabasco? (Morelet’, Hoge); San Juan Bautista, Tabasco (H. H. 
Smith). 
Yucatan (Morelet*); Carmen Island®, at the Laguna de Terminos (Sallé and 
Cloué *). 
Var. helictomphala. 
Helix helictomphala, Pir. P. Z. 8. 1856, p. 877°; Malak. Blatt. iii. p. 280 (1856) ’; Monogr. Helic. 
Vivent. iv. p. 314°. 
Helix (Polygyra) helictomphala (Pfr.), Fisch. & Crosse, loc. cit. p. 272, t. 12. figg. 10, 10 a-c’. 
Polygyra helictomphala (Pfr.), Strebel, Beitr. Mex. Land- und Siissw.-Conch. iv. p. 46, t. 15. 
fig. 11°. 
Hab. 8.K. Mzxico: San Juan Bautista, Tabasco (H. LH. Smith). 
Cuiapas (Ghiesbreght —*), 
A specimen obtained by Hége in Tabasco proves that P. yucatanea, Morel., and 
P. helictomphala, Pfr., belong to one and the same Species, an affinity previously sus- 
pected by Fischer and Crosse. This shell is quite flat above, and the upper external 
tooth is distinctly larger than the lower one; in all other respects, especially in the 
costulation, it fully agrees with a specimen of P. helictomphala given by Cuming to 
