164 MOLLUSCA. 
of South America, and the species are less numerous on the Caribbean Islands than in 
Florida and Texas. Within our limits the southernmost is P. dysont, in Honduras. 
In N.W. Mexico there are some species of comparatively large size and peculiar modi- 
fication of the apertural teeth, for instance, P. acutedentata. ‘Two other modifications 
found in the Southern States of North America are not yet known from Mexico, viz., 
the very flat and multispiral species, such as P. cereolus, Meg., and P. septemvolva, | 
Say, in Florida, and those in which the upper external tooth of the aperture is situated 
somewhat deeper inward, as if pushed back by the prominent tips of the strong parietal 
fold, such as P. troostiana and P. dorfeuilleana, Lea, P. fastigans, Say, and P. hazardi, 
Bland, which are the characteristic forms in Tennessee and the adjacent regions. 
1. Polygyra implicata. (Tab. VII. figg. 5, 5 a-c.) 
Helix (Dedalochila) implicata, Beck, Index Moll. 1838, p. 21 (sine descr.) *. 
Helix implicata (Beck), v. Mart. in Malak. Blatt. xii. p. 20 (1865) *; Pfr. Monogr. Helic. Vivent. 
v. p. 421°, . 
Helix (Polygyra) implicata (Beck), Fisch. & Crosse, Miss. Scient. Mex., Mollusca, i. p. 283, t. 12. 
figg. 12, 12 a-c*. 
Polygyra implicata (Beck), Strebel, Beitr. Mex. Land- und Siissw.-Conch. iv. p. 47, t. 3. figg. 1 
a-h (* a young shell), p. 48 (anatomy) ’. 
Helix oppilata, Pfr. Monogr. Helic. Vivent. iv. p. 314°; Binney & Bland, Land and Fresh-water 
Shells of N. Am. i. p. 101, fig. 177 (ex parte, nec Morelet) *. 
Hab. ¥. Mexico: Rio Tecoluta, in the State of Vera Cruz, about 21° North Lat., near 
the shore (Deppe?*+); Agua Caliente, Rancho Guerrero, an island in the Rio 
Palpoala, Camino de Arroyo Hondo, and Camino de Obispo, all near Misantla 
(Salas°) ; Barranca de Mahuistlan, between Jalapa and Mirador, and San Juan 
Miahuatlan, at the roots of trees under rotten leaves (Strebel®); Jalapa (/lége) ; 
Vera Cruz, dead shells only, in alluvial deposits (Uhde?*, Friedel 2.4, and Strebel ®) ; 
Mexico, without nearer indication of locality !. 
SoutH CentraL Mexico: Oaxaca (Hége). 
The specific name signifies ‘‘ inwardly-folded,” not, as one might suppose, “not 
folded,” and refers to the aperture. The very open umbilicus and the two nearly equal 
external teeth are the chief characteristics of this species. 
2. Polygyra oppilata, | 
Helix oppilata, Morelet, Test. Noviss. i. p. 8 (1849) *; Pfr. Monogr. Helic. Vivent. iii. p. 264°. 
Helix (Polygyra) oppilata (Morel.), Fisch. & Crosse, Miss. Scient. Mex., Mollusca, i. p. 285, t. 12. 
figg. 11, ll a-c’. 
Polygyra oppilata (Morel.), Strebel, Beitr. Mex. Land- und Siissw.-Conch. iv. p. 49, t. 3. 
figg. 2 a—-d*. 
Hab. EK. Mexico: Vera Cruz, only in alluvial deposits (Strebel *). 
