LAMELLIBRANCHIATA. 345 



Valves moderately convex, slightly gibbous in the umbonal region. 



Beaks small, situated a little more than one-third the length from the 

 anterior end. Umbonal slope marked by two distinct furrows, which are 

 limited by three rather sharply angular carinae, one very near the cardinal 

 line, one along the umbonal angle, and another one intermediate and equidis- 

 tant. 



Surface marked by coarse, regular, elevated, concentric folds which are 

 strongly undulated as they cross the ridges and depressions of the posterior 

 slope. 



A specimen of normal form has a length of 14 mm. and a height of 8 mm. 



This is a comparatively rare form, and is most nearly allied to P. emarginata, 

 but differs in the characters of the posterior slope ; that species having a single 

 very deep sulcus, while this one has two shallower sulci, the upper one extend- 

 ing nearly to the cardinal line. 



Formation and locality. In the Chemung group, near Elmira, N. Y. 



Pal^oneilo elongata. 



PLATE XLVm, FIG. 39 ; AND PLATE XCIII, FIG. 11 a. 

 PakBoneilu elongata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations ; PI. 48, fig. 39. 1883. 



Shell small, very elongate-ovate, attenuate posteriorly; length twice the 

 height ; basal margin regularly and gently convex, curving abruptly upward 

 at the anterior end. Posterior extremity abruptly rounded or sub-truncate. 

 Cardinal margin arcuate, anterior end regularly rounded. 



Valves depressed-convex below and posteriorly, more convex above the 

 middle in the anterior and umbonal regions. 



Beaks situated behind the anterior third, small, not prominent. Umbonal 



ridge undefined. 



Surface marked by very fine, even, slightly undulating concentric striae. 



Interior unknown. 



Three specimens measure respectively 16, 14 and 13 mm. in length, and 



7, 7 and 6.5 mm. in height. 



