171 



The margin is truncated by a flat band, about half a line in -widtli and 

 nearly vertical, sloping a little in-ffards and upwards. On the under side 

 the whorls are strongly convex, obscurely angulated at the edge of the 

 umbilicus ; there are indications of a faint concave band just below the 

 margin. Umbilicus small ; when measured across from the angulated line 

 tDf the last whorl, it is one-third the whole width, but it contracts to one- 

 tenth the whole width in passing through this whorl, and seems to diminish 

 only slightly thence to the apex. The whorls in the umbilicus are rounded. 

 The aperture is sub-circular ; rounded on the inner and lower side, and 

 angular at the edge, its height about equal to its width. The second 

 whorl is slightly turretted above the last. Surface with fine and coarse 

 striae, the latter being minute undulations of growth, about four in one 

 line, all curving backwards to the margin both above and below. 



Width, from 10 to 12 lines ; height, from 7 to 9 lines. 



Locality and Formation. — Pauquette's Rapids, on the Ottawa River ; 

 Black River limestone. 



Collector. — E. Billings. 



Pledeotomaria Vitruvia. (N. sp.) 



Description. — Shell sub-lenticular ; spire depressed conical, smooth ; 

 apical angle from 120° to 130° ; whorls three. On the upper side the 

 whorls make a nearly smooth flat slope from the apex to the margin, which 

 is narrowly rounded, and shows some indications of a band. Below the 

 margin convex, gradually increasing in prominence to the edge of the 

 umbilicus which is rather sharply angulated. In the umbilicus the whorls 

 are nearly flat, and sometimes forming an indistinct staircase to the apex. 

 The umbilicus is about one-third the whole width, abruptly ascending 

 from the angulated edge to the apex. Surface nearly smooth. 



The whole of the aperture has not been observed, but several silicified 

 fragments show that the inner lip is nearly straight and approaching the 

 vertical, slightly convex in its upper, and concave in the lower half, giving 

 an obscure sigmoid curve. It is much extended downwards, making the 

 depth of the body whorl at the angle of the umbilicus at the aperture 

 more than one-third the whole height of the shell. 



Width from 12 to 18 lines ; height from 9 to 12 lines. 



This species is allied to both P. A^uericana and P. Progne, but difi^rs 

 from the former in having the whorls flat in che umbihcus instead of 

 rounded, while the latter has the umbilicus closed. 



Locality and Formation. — Pauquette's Rapids, on the Ottawa River ; 

 Black River limestone. 



Collector. — E. Billings. 



