1903.] NATURAL SCIENCES OF PHILADELPHIA. 207 



Key to average or normal specimens of Paravitrea. 



I. — Surface closely and regularly rib-striate or grooved, at least above; 

 umbilicus minute. 

 a. — ^Diam. 5-6.5 mm. ; spire flat or slightly convex, the suture deep ; 

 6^ convex, narrow whorls, subregularly and deeply grooved 

 radially, above and below. Umbilicus minute. No in- 

 ternal teeth, V, clappi. 



a'. — Diam. 2.5 to 3.5 mm.; very closely rib-striate above; 

 whorls 5^-6, closely coiled, the spire but slightly convex. 

 b. — One to three radial rows of 5 or 6 teeth each, visible through 



the base, T^. multidentata . 



h' . — One to three radial curved barriers, visible through the 

 base; surface not striated spirally; width of umbilicus 

 about one-tenth that of the shell, . . V. lamellidens. 

 6".— With barriers like the preceding species, or none; surface 

 finely striate, the stria? decussated by very minute 

 spirals; umbilicus wider, its diameter contained about 

 5^ times in that of the shell, V. walkeri. 



II. — Surface sculptured with spaced, unequal radial grooves, more 

 ' conspicuous above. 



a. — Diam. of adults 5 to 6 mm. ; toothless or with teeth in pairs. 

 b. — Periphery median; aperture usually crcscentic. Eastern 

 forms. 



c. — Shell toothless, V. capsella. 



c' . — Shell with internal pairs of teeth, . Y . c. lacteodens. 

 b' . — Western forms (Missouri, Arkansas, Indian Territory), 

 with the aperture subtriangular. 

 c. — -Young usually toothed; adults dome-shaped, with 



subbasal periphery V.significans. 



c'. — Not toothed; adults discoidal, . . . V.simpsoni. 

 a'. — Diam. of adults 7 to 7^, mm. ; toothless or with 1 to 5 teeth in 

 each row. 

 b. — No teeth at any stage of growth; wJiorls 7 to 7h, 



V. placentula. 



b' . — Teeth developed in young shells, persisting or absent in 



adults; shell very fragile; luhorls S to Sh, V. andrewsce. 



Titrea clappi (Pils.). PL X, figs, l, la, lb, 8, 6a. 



Gastrodonta clappi Pils., Nautilus, XII, p. 86 (December, 1898); XV, p. 37, 

 PI. 2, figs. 8, 9 (August, 1901); Proc. Acad. Nat. Sci. Phila., 1900, p. 144. 

 Ferriss, Nautilus, XII, p. 99; XV, p. .58. 



Range : Great Smoky Mountains, along the Tennessee-North Caro- 

 lina boundary range from Thunderhead and Blockhouse Mountains to 

 the Big Pigeon river. 



The type locality is Miry Ridge. The type (PI. X, figs. 1, la, lb), 

 with a diameter of 5,5 ram., has a minute umbilicus, about .2mm. wide, 

 and the spire of 7 whorls is convex. In all other specimens seen the 



