170 



Pleukotomakia Agave. (N. sp.) 



Fig. 153. Fig. 154. 



Fig. 153. — Pleurolomaria Agave. 



154. — F Dryope. a and b, different Tiews of tlie same specimen. 



Drycrqition. — Lenticular, with an acute margin ; apical angle from 

 12.3 "^ Lo 1 4.3° ; -whorls three, forming a nearly smooth slope from the apex 

 to the margin. On the upper side the last ivhorl is gently concave in the 

 outer half, or two-thirds of the width, and slightly convex or flat above ; 

 in some specimens the concavity occui^ies the whole width ; upper whorls 

 gently convex or flat ; apex generally rounded. The margin in the last 

 whorl is thin, sharp, and a little turned upwards. On the underside the 

 whorls are convex, most prominent a httle within the mid-width where 

 they are obtusely rounded angular. Umbilicus a little more than one- 

 third the whole width, exposing the rounded inner edges of all the whorls 

 to the apex. Aperture rhomboidal. Sui-face with fine striae curving 

 backwards to the marg-n. 



Width of an average specimen 22 lines ; height 10 lines ; width of 

 last whorl, on the upper side at the aperture, 7 lines. The width appears 

 to be from 15 to 24 lines ; the most common 20 lines. 



P. hqjickla (Salter) is smaller and has the aperture more nearly 

 elliptical, and a much narrower umbihcus. 



P. Americana (Billings) has the outer margin rounded. 



P. tqjerta (Salter) has the whorls more slender, and the umbilicus 

 •wider. 



Lornltti/ andFormation. — Naquareau Eiver, above Red River; Trenton 

 limestone. 



Collector. — J. Richardson. 



Plburotomaria Dryope. (N. sp.) 



Pig. 154. a, b. 



Description. — Shell turbinate ; spire depressed conical ; apical angle 

 about 100° ; whorls three. On the upper side the whorls are concave for 

 three-fourths their width ; the inner one-fourth next the suture convex. 



