OF NORTH AMERICA. 



sculpture (see pi. XLIX, fig. H) ; sutures deeply indented; aperture 

 very elongate-ovate, somewhat produced anteriorly ; peristome thin, 

 acute ; inner lip reflected over the umbilical chink to form a thin, narrow 

 expansion, which is usually appressed to the umbilical region, giving 

 the axis a slight twist ; parietal callus very thin ; umbilical chink vary- 

 ing from distinctly open to scarcely observable ; the surface of the 

 shell is frequently malleated. 



Breadth. Aperture length. Breadth. 



Locality. 

 Type of obrussa 



philadelphica 



a a 



" acuta 



Length. 



9.50 4.50 5.00 2.50 



8.00 4.50 4.00 2.00 



9.00 5.00 4.50 2.00 



15.00 6.00 7.00 2.75 



14.00 6.00 6.50 3.00 



18.00 7.75 9.00 3.75 



17.00 8.00 10.00 4.00 



19.50 12.50 12.50 7.28 



18.25 9.00 10.00 5.00 



14.00 6.00 7.15 3.25 



13.50 6.50 7.00 3.50 



11.00 5.00 6.00 3.00 



13.25 7.25 7.25 4.00 



12.00 5.50 6.25 3.25 



12.50 6.50 6.50 3.50 



11.00 5.00 5.75 3.25' 



12.00 6.00 6.00 3.00 



13.00 5.75 7.50 4.00 



12.00 7.10 7.00 4.00. 



13.00 6.50 7.00 3.50 



17.50 8.00 8.50 4.50 



16.00 8.00 9.00 5.00 



17.75 7.75 9.00 5.00 



TYPES: Obrussa Say, two specimens, Acad. Nat. Sci Phil., No. 

 58700 ; philadelphica Lea, Smithsonian Institution, three specimens, 

 No. 118687; acuta Lea, three specimens, Smithsonian Institution, Lea 

 Coll., No. 118643. 



TYPE LOCALITIES : Obrussa, Harrowgate, Philadelphia County, 

 Pennsylvania ; philadelphica, River Schuylkill, near Philadelphia ; acuta, 

 pond four miles north of Philadelphia. 



ANIMAL: With a very small, more or less oblong foot, when 

 viewed from the base, the anterior and posterior borders rounded ; color 

 dark gray or blackish, lighter below, sometimes yellowish, the whole 

 surface is dotted with whitish or yellowish, which is specially notice- 

 able about the eyes ; tentacles triangular, flat, short, more or less trans- 

 parent; the black eyes are placed on prominences at the inner base 

 of the tentacles ; respiratory orifice on the right side, near the angle 



Haldeman's figure 14 



7 

 2 

 Owasco Lake, N. Y. 



Joliet, 111. 



Des Moines, la. 



a a 



Chicago, 111. 



Lemont, 111. 



(i a 



Bethlehem, Pa. 

 Lebanon, Pa. 



