TTNIVERSALLY DISTRIBUTED SPECIES. 65 



cepting- from Portland, Oregon, 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 external generic characters. 



Jaw arcuate, ends attenuated, pointed ; concave margin smooth, with 

 a median rounded projection. ■ fig. 22. 



Lingual membrane (T. M., Y.Plate 

 III, Fig. E). Morse gives 54 rows of 

 27-1-27 teeth each. I have figured 

 the central and first lateral, with 

 one extreme marginal tooth, drawn j&w of z. viriduUis. (Morse.) 



from a specimen furnished ^e by Mr. Allen of Orono, Me. I find 3 

 lateral teeth. Morse gives a similar figure. The European Z.viriduluft, 

 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 num- 

 ber of whorls, and the rapid enlargement of the largest whorl, this 

 shell corresponds with Z. indentatus. It differs in its darker, smoky 

 horn-color, its constant umbilicus, its rather thick and shining peri- ' 

 stome, and in its. whitish wrinkles, which, instead of being remote, are 

 crowded. From arboreus it differs in having 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 umbilicus. In 

 arboreus the peristome has a flexuous curve, but is nearly a direct sec- 

 tion of the whorl in this. Though all of the same size and general 

 appearance, the three may be readily separated when mingled. In- 

 deed, its claims as a distinct species are not very obvious without view- 

 ing the three together. It is found abundantly under fragments 

 of wood, in damp places near the water's edge, in company with Z. 

 fulvus and arboreus^ and Vertigo modesta. On its upper surface it ap- 

 pears to be identical with Z. indentatus, while on the base its resem- 

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

 and very common species. 



Mr. Gwyn Jeffreys calls the American form Z. radiatulus var. albus 

 (Ann. Mag. iT. H., 1872, 245). 



Genitalia unknown. 



1749— Bull. 28 5 



