552 UNITED STATES GEOLOGICAL SURVEY OP THE TERRITORIES. 



Helix vctusla, M. & H. 



Plate 42, figs. 7, a, b. 



Helix ritrinoides, Meek and Hayden (1857), Proceed. Acad. Nat. Sci. Philad., IX, 135 (not H. ritrinoides, 



Desbayes, 1830). 

 Helix retusta, Meek aud Hayden (1860), Proceed. Acad. Nat. Sci. Philad., XII, 431. 



Shell subglobose, breadth and height nearly equal, or the former some- 

 what greater than the latter; spire rather prominent; volutions about four, 

 increasing rather rapidly in size, last one ventricose, rounded, and slightly 

 constricted at the aperture; umbilical depression (in casts) small, probably 

 closed by the spreading of the inner lip ; aperture higher than wide, appar- 

 ently subovate, a little oblique, and somewhat declining ; lip reflexed ; suture 

 well defined. (Surface unknown.) 



Height, 0.40 inch ; breadth, 0.43 inch ; length of aperture, 0.26 inch ; 

 breadth of same, 0.20 inch. Other specimens of apparently the same 

 species are nearly twice as large as the figured and measured example. 



I have only seen casts of this species, and consequently know nothing 

 of its surface-markings. The constriction mentioned in the body-whorl near 

 the aperture may possibly have been produced in the cast by an internal 

 thickening of the lip, though it has the appearance of having been accom- 

 panied by a corresponding constriction of the exterior, around the reflected 

 margin. There are also on the cast apparently some indications of an 

 obscure mesial linear angle on the outer side of the body-whorl, which 

 angle, however, becomes obsolete near the aperture. 



As stated in another place, it is barely possible that the form described 

 in this report under the name Vitrina ohliqua may bean accidentally-depressed 

 specimen of this species ; though I think not, as that type seems to have its 

 body-volution more rapidly expanded. 



The shading on our figure 7, b, plate 42, of this species, gives an appear- 

 ance of obscure revolving striae, that do not exist on the specimens, all of 

 which are mere internal casts. 



Locality and position. — Mouth of Judith River, on the Missouri; from 

 the Judith River Fresh- and Brackish-water beds; probably belonging to the 

 closing period of the Cretaceous. 



