MIOCENtf MOLLUSCA AND CKUSTACEA. 61 



in lines, leaving narrow raised ridges at regular intervals, parallel to the 

 margin of the valve, which present the appearance of strong raised varices. 

 So prominent and constant a feature is this that it might readily be mis- 

 taken for a specific feature of the shells and as indicating a second species. 

 The lunule and escutcheon are both proportionally deep and narrow, with 

 very sharply raised edges. 



I have seen the species as yet only from near Shiloh, N. J. 



Family UNGULINID^]. 



Geuus MYSIA Leach. 



Mysia parilis. 



Plate ix, figs. 9-13. 



Mysia parilis Conrad; Am. Jour. Couch., vol. 2, p. 71, PI. IV, fig. 1; Heilpriii, Tert. 

 Geol. U. S., p. 8; Proc. Acad. Nat. Sci., Phil., 1887, pp. 397, 403. 



"Equilateral, nearly circular, ventricose, thin, and fragile; basal and 

 anterior margin regularly rounded." (Conrad.) 



Shell small, nearly circular in outline, being very slightly longer than 

 high, and as shown by a single specimen, a little more than two-thirds as 

 thick as long. Beaks very small, rising but little above the cardinal line, 

 the umbones, however, becoming a little more prominent, the beaks situated 

 a very little forward of the middle of the valve; disk of the valves regu- 

 larly rounded throughout, and the surface smooth or marked only by fine 

 lines of growth. 



A single imperfect valve forms the typical material of this species. It 

 is imbedded in marl and is much broken at the apical portions, some of 

 which, including the beak, have been lost. From it the characters of the 

 interior can not, therefore, be obtained. A smaller left valve, and a frag- 

 ment of a right valve from another collection, show the shell to be thin 

 and the hinge narrow, with two teeth in each valve. In the left valve the 

 anterior tooth is elevated, deeply bifid, and recurved, the posterior' being 

 single, low, and very oblique; the space between occupied by a deep pit. 

 In the right valve the anterior tooth is single, oblique, and inconspicuous, 

 and the posterior very small, short, and distinctly bifid; the pit between 



