MIOCENE MOLLUaOA AND CliUSTAGEA. 61 



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

 margrii 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 })ro])ortioiially deep and narrow, with 

 very sharply raised edges. 



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



Family UNGUJLINin^E. 



Genus MYSIA Leach. 



Mysia parilis. 



I'liite IX. flf-s. 1)-13. 



iMysitt ji<(rili.i Oourad; Am. -lour. Couch., vol. 2, p. 71, PI. iv, fig;. 1 ; Ileiliuiu, Tert. 

 (leol. IT. S., p. 8; Piw. Acad. Nat. Sci., Phil., 1887, pp. .•5!»7, 403. 



"E(piihiteral, nearlv 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 b\' a, single specimen, a little mon; than two-thirds as 

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

 the umboues, however, becoming a little more })rominent, the lieaks situated 

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

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

 lines of growth. 



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

 is imbedded in marl and is much l^roken at the a[)ical ])ortioiis, some of 

 which, including the l)eak, 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 Ije thin 

 and the hinge naiTOw, Avith two teeth in each valve. In the left valve the 

 anterior tooth is elevated, deeiily 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 bitid; the pit between 



