GASTROCOPTA, NORTH AMERICA, WEST INDIES. 53 



Length 2.5, diam. 1 mm. 



Maine and Ontario to Minnesota, south to St. Simon's 

 Island, Georgia, northern Alabama and Alexandria, Louisi- 

 ana. Type locality, Philadelphia, Pa. 



Odostomia corticaria SAY, Nicholson's American Encyclo- 

 pedia, ii, pi. 4, fig. 5, 1816. Pupa corticaria, Say PPEIFFER, 

 Monogr. Hel. Viv., ii, 228; vi, 304. BINNEY, Terr. Moll., ii, 

 p. 339, pi. 72, f. 4. W. G. BINNEY, Terr. Moll., v, 1878, p. 

 209, f. 113, 114, pi. 72, f. 4. Leucochila corticaria Say, 

 MORSE, Terr. Puhn. Maine, p. 36, f. 87, pi. 10, f. 88. 



G. corticaria has the teeth more reduced than in any other 

 Gastrocopta. The angular lamella is variable, sometimes 

 rather well developed, as in figures 1, 4, sometimes minute, 

 and scarcely united with the parietal lamella, and in some 

 apparently mature shells it is entirely wanting. The very 

 low columellar lamella runs vertically 011 the back of the 

 rather large axis, and either turns outward in a short hori- 

 zontal limb at the lower end, or a very low tubercle, visible 

 from in front, stands in front of its lower end (pi. 10, fig. 3). 



As the name denotes, G. corticaria is often found crawling 

 upon trees a foot or two from the ground. While generally 

 distributed, it rarely occurs in abundance, and is not known 

 from the higher Catskills, southern Alleghanies, or other ele- 

 vated regions. So far as I have seen specimens, its western 

 limit is in Minnesota, Iowa and Arkansas. No local or geo- 

 graphic races have been noticed. 



Subgenus GASTROCOPTA Wollaston. 



Gastrocopta WOLLASTON, Test. Atlant., 1878, p. 515. Bifi- 

 daria STERKI in Pilsbry, Proc. A. N. S. Phila., 1891, p. 315. 

 Eubifidaria STERKI, Nautilus, vi, p. 101, 1893, type "P. 

 hordeacea Gabb" of Sterki, = G. cristata (Pils. & Van.). 



The shell is rimate, cylindric or oblong-conic, having the 

 angular and parietal lamellae concrescent into a sinuous or 

 bifid lamella; columellar lamella horizontal, short. Palatal 

 folds not standing upon a callous ridge, the upper and basal 

 sometimes wanting, the basal, when present, in the base of 

 the aperture, not subcolumellar in position. 



