HEMICTCLONOSTA. 167 



culum ; a tliin epidermis. — Obs. The land shells composing this 

 genus are found in all parts of the world; the common snail, 

 H. Aspersa, is well known as a destructive animal in our gardens. 

 The genera Helix, Achatina, Bulinus, Clausilia, Anostoma, &c., 

 have been united under one generic name by De Ferussac, and 

 again divided under the following sub-generic names, each of 

 which we shall illustrate by a figure. Gtenus Helix : Sub-genus 

 1, Helicophanta, consisting of species with large apertures, like 

 Yitrina ; Helix brevipes. >S'. gen. 2, Cochlohydra, Succinea 

 Amphibia, Drap. S. gen. 3, Helicogena, consisting of the 

 common species vsdth the last whorl large ; Helix Hsemastoma, 

 H. Contusa, (Streptaxis, Grray,) H. Aspersa. S. gen. 4, Helico- 

 donta, consisting of species with teeth or folds on the columella ; 

 Polydonta, Montf. Anostoma, Helix Nux-denticulata. S. gen. 5, 

 Helicigona, Carocolla, Greotrochus. S. gen. 6, Helieella, consist- 

 ing of depressed species with a large umbilicus ; H. Citrina 

 (Naninia, Grray.) S. gen. 7, Helicostyla, consisting of species 

 with a simple aperture, like the Helicogense, but with the whorls 

 increasing very gradually ; H. epistylium. S. gen. 8, Cochlostyla, 

 Bulinus. S. gen. 9, Cochlitoma, Achatina. S. gen. 10, Cochlicopa, 

 Polyphemus Glaus. ;S. gen. 11, Cochlicella, Bulinus decollatus. 

 S. gen. 12, Cochlogena, Azeca tridens. S. gen. 13, Cochlodonta, 

 Pupa Uva. S. gen. 14, Cochlodina, Clausilia macascarensis, 

 Balea fragilis. The last three sub-genera are included in the 

 genus Odostomia of Plemiug. "We give an example of each of 

 these sub-divisions, for the sake of presenting the reader with 

 the principal variations to which the genus is subject. The 

 established genera will be characterized in their places. PL xiii. 

 fig. 254 to 281, 



HELIXAEION. Perussac, 1819. Viteina, Drap. Difiering 

 from Helicolimax in the structure of the animal. PI. xiii. fig. 262. 



HEMICAEDITJM. Swainson, 1840. {hiJ^LavQ, hemisus, half, 

 Kapdia, cardia, heart.) Caedium Hemicardium, and several 

 similar species. PL vi. fig. 123***. 



HEMICTCLA. Sw. A sab -genus of Helix. 



HEMICYCLONOSTA— see Caedilia. 



