116 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



been found from Great Slave Lake to the Gulf of Mexico; in the Central 

 Province, in Arizona, Colorado, and New Mexico. I have not actually, as yet, 

 received it from the Pacific Province, but have no doubt it will be proved to 

 inhabit all the North American continent. 



Animal bluish-black. I have not verified the existence of a caudal pore or 

 other generic characters. 



Jaw arcuate, ends attenuated, pointed; concave margin smooth, with a me- 

 dian rounded projection. 



Lingual membrane (PI. III. Fig. E). Morse gives 54 rows of 27 — 1 — 27 

 teeth each. I have figured the central and first lateral, with one extreme mar- 

 ginal tooth, drawn from a specimen furnished me by Mr. Allen of Orono, 

 Me. I find 3 lateral teeth. Morse gives a similar figure. The European 

 Z. virididus as figured by Lehmann (Z. purus) has a similar dentition, 

 excepting size of central tooth ; he gives 23 — 1 — 23 teeth, with 3 laterals. 

 •There are distinct side cusps as well as cutting points to centrals and laterals. 



In size, the depressed-conical shape of the upper surface, the number of 

 whorls, and the rapid enlargement of the largest wborl, this shell corresponds 

 with Z. indentatus. It differs in its darker, smoky horn-color, its constant um- 

 bilicus, its rather thick and shining peristome, and in its whitish wrinkles, 

 which, instead of being remote, are crowded. From arboreus it differs in hav- 

 ing one whorl less, the last one rapidly dilating, its apex not being depressed, 

 its thinner structure and more glossy surface, and in its somewhat smaller um- 

 bilicus. In arboreus the peristome has a flexuous curve, but is nearly a direct 

 section of the whorl in this. Though all of the same size and general appear- 

 ance, the three may be readily separated when mingled. Indeed, its claims as 

 a distinct species are not very obvious without viewing the three together. It 

 is found abundantly under fragments of wood, in damp places near the water's 

 edge, in company with Z. fidvus and arboreus, and Vertigo modesta. On its 

 upper surface it appears to be identical with Z. indentatus ; while on the base 

 its resemblance to Z. arboreus is striking. It appears to be a widely diffused 

 and very common species. 



Mr. Gwynn Jeffreys calls the American form Z. radialulus var. albus (Ann. 

 Mag. N. H. 1872, 245). 



Genitalia unknown. 



Zonites indentatus, Say. 

 Vol. III. PI. XXIX. Fig. 2. 



Shell subperforated, flattened, thin, pellucid ; epidermis highly polished, cor- 

 neous ; whorls rather more than 4, rapidly enlarging, with regular, subequi- 

 distant, radiating, impressed lines, which on the body-whorl extend to the 

 centre of the base, outer whorl expanding towards the aperture ; suture well 

 impressed ; aperture rather large, transverse ; peristome simple, acute, very 

 thiil, at its inferior extremity terminating at the centre of the base of the shell ; 



