GUELPH FAUNA IN THE STATE OF NEW YORK 55 



tural expansion in neanic, ephebic and gerontic conditions. They permit, 

 therefore, the addition of some important facts to the description of that 

 species. 



Description. Shell subdiscoid, involute ; whorls three to four ; in 

 section subcircular to roundly elliptic, with inner groove, the outer whorl 

 being impressed on the inner. The aperture has a flaring lip, which is 

 turned outward by rather abrupt curvature till it stands at right angles to 

 the axis of the body whorl and is then reflected. This lip attains, in one 

 specimen, in its longer axis, a length of 65 mm, and in its minor one a 

 length of 50 mm. The inner lip was folded back over the last whorl to 

 such an extent that it covered about one third of it. 



Most transverse sections of the shell show symmetric enrolment of the 

 whorls, but a few, undisturbed in their growth, evince indications of asym- 

 metry in early growth. This condition, however, has not been demonstrated 

 a normal feature. 



The degree of involution seems to have been subject to some variation, 

 as there is some difference in the specimens in the width of the umbilicus 

 at full growth. In the great majority, however, the volutions embrace suf- 

 ficiently to make the umbilicus relatively small. The whorls are abruptly 

 convex around the umbilicus. 



The surface ornamentation consists of about 20 coarse flat topped 

 revolving ridges, on each side from keel to umbilicus ; these are separated 

 by equally wide furrows with generally a smaller rib between them. The 

 ribs have a somewhat irregular undulating course, periodically swelling and 

 contracting, giving the surface a peculiarly irregular appearance. These 

 irregularities are caused by intersection with incised concentric lines, 

 beyond which the revolving ribs appear out of position. The ribs are also 

 intersected by broad, transverse folds, which curve obliquely backward 

 across the whorls. These are most distinct near the umbilicus and become 

 faint near the dorsal keel. On the outside of the peristome the ribs 

 become quite abruptly coarser ; and in gerontic specimens they change, on 

 the outer lip, into broader, less keeled ribs, and the smaller intercalated 



