156 Trans. Acad. Set. of St. Loxiis. 



species, figured by Prof. Harris on the same plate as the 

 young of P. servatoidea Aid., with which it evidently has no 

 relationship. This latter species seems in fact to be ex- 

 ceedingly close to georgei, and appears to be from the same 

 horizon. Microsurcula will include, in addition, the Upper 

 Claiborne Pusus vetustus, of Lea, and two species from the 

 Vicksburg Oligocene, one of which I recently described under 

 the name P. intacta. 



Lyrosurcula n. gen. 



The species of this genus bear some resemblance to those 

 of Pleurofusia, but the spire whorls and ribbing are more 

 cylindrical and the spiral lyrae are different in character, 

 being equal and equally spaced among themselves below the 

 fasciolar surface and not enlarged on the ribs to anv very 

 noticeable degree. They differ also in the embryo, which, 

 although conical and multispiral, has the lower whorl or two 

 covered with longitudinal riblets, these being absent in Pleuro- 

 fusia. The three species at present before me may be 

 recognized by the following characters : — 



Embryo acutely conical, higher than wide, of 6 whorls, the apical or nucleus 

 more swollen and slightly eccentric, the first three smooth, the lower 

 three covered with very regular riblets which at first are very fine, 

 close- set and feeble, becoming gradually coarser and more widely spaced, 

 the sixth whorl gradually acquiring the spiral lyrae, these appearing 

 distinctly between the riblets ; fasciolar surface beginning abruptly at 

 the end of the sixth whorl; next two whorls — the first two body 

 whorls — having strongly rounded outline, about eleven feebly elevated 

 and transversely rounded subcylindric ribs, three strong but narrow, 

 well separated spiral lines in rather more than basal half and a decliv- 

 ous, broadly concave fasciolar surface, with distinct arcuate lines of 

 growth and two fine spiral threads and not entirely crossed by the 

 rapidly obsolete ribs; subsutural collar very small and feebly carinulate ; 

 canal short, slender and twisted. Length of a specimen having a com- 

 plete exbryo and 2 body whorls, 4.3 mm.; width, 1.6 mm. Lower 

 Claiborne Eocene of St. Maurice, La - . elegans n. sp. 



Embryo less acute at tip, a little higher than wide, of four whorls, the upper 

 three smooth, the fourth alone with a few widely separated, obliquely 

 arcuate and rather feeble riblets, body whorls nearly as in the preced- 

 ing, with ten broadly rounded ribs distinct in the inflated subcylindric 

 lower half of the whorls and scarcely intruding at all upon the steeply 

 descending and broadly concave fasciolar surface; the sculpture 



