476 PALEONTOLOGY OF NEW YORK. 



Phthonia lirata. 



PLATE LXXVIII, FIG, 14. 

 Phthunia lirata. Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 78, figf. 14. 1883. 



Shell small, elongate-elliptical ; length more than twice the height. Basal 

 margin regularly and gently curved. Posterior extremity regularly rounded. 

 Cardinal line nearly straight. Anterior end short, regularly rounded. 



Valves regularly convex, approaching to gibbous in the umbonal region. 



Beaks sub-anterior, low and appressed, scarcely rising above the hinge-line. 

 Umbonal slope regularly rounded, not defined. 



Surface marked by fine concentric striaB, crossed by distant radii, which 

 are less frequent on the middle of the shell and obsolete on the anterior end. 



The cardinal margin, just below the hinge-line, on the interior of the valve 

 is marked by two slender grooves. 



The specimen described has a length of 8 mm. and a height of 3.5 mm. 



This species is distinguished by its regular elliptical form, its small size and 

 slender, distant radii. 



Formation and locality. In the Hamilton group at Norton's landing, Cayuga 

 lake, N. Y. 



Phthonia truncata, n. sp. 



PLATE XCrV, FIG. i. 



Shell above the medium size, sub-trapezoidal ; length twice the height as 

 measured at the posterior extremity. Basal margin nearly straight, abruptly 

 recurving at the post-inferior extremity and curving upward in front. 

 Posterior extremity in the lower part almost vertically truncate, obliquely 

 truncate above. Cardinal line oblique, rising toward the posterior end. 

 Anterior end short, abruptly rounded. 



Valves depressed-convex along the basal portion and on the post-cardinal 

 slope, somewhat gibbous in the umbonal region. 



Beaks sub-anterior, small, appressed, rising very little above the hinge line. 

 The shell at the umbo is slightly flattened, and this feature is continued to 



