294 PALEONTOLOGY OF NEW YORK. 



extremity. Between the umbonal ridge and the cardinal line the shell is 

 concave. 



Test of moderate thickness. Surface marked by fine regular concentric 

 striae, which are sometimes thickened on the lower side of the shell. In a 

 well-preserved specimen the valves below the umbonal angles are marked by 

 fine radiating striae, which are more conspicuous posterior to the sinus. The 

 test on the umbonal ridge is elevated into a sharp crest. 



Anterior muscular impression immediately below the beaks and close to 

 the anterior margin of the shell. Pallial line not deepl}^ impressed. Poste- 

 rior muscular scar strong, situated on the cardinal slope near the margin, 

 leaving a shallow groove in its advance from just behind the beaks. Liga- 

 mental groove very strong. 



A specimen of medium size has a length of 46 mm. and a height of 24 

 mm. A smaller individual measures 43 mm. in length and 20 mm. in height. 



In its anterior beaks and narrow posterior end this species resembles G. acuta, 

 but the cardinal line is much shorter than in that form, the basal margin is 

 less strongly sinuate and the umbonal ridge is not regularly arcuate. Compared 

 with G. truncata, the umbonal ridge is more distinctly curving, the cardinal 

 slope is concave, the radii are finer and more closely arranged. 



Formation and locality. In the Schoharie grit, at Schoharie, N. Y. 



GONIOPHORA ? ALATA, n. sp. 

 PLATK XXXIV, FIG. 7 ; AM> PLATE XI.II, FIG. 3. 



Shell large, trapezoidal ; length less than twice the height ; basal margin 

 nearly straight ; posterior margin very broad, truncate ; anterior end short, 

 small, limited posteriorly by an undefined sinus. 



Valves convex below, gibbous on approaching the umbo, and depressed 

 above the umbonal ridge, with an undefined furrow extending from a point 

 anterior to the beaks to the posterior margin. 



Hinge-line straight, oblique, about one-third the length of the shell. 



Beaks anterior, small and acute. Umbo prominent, angular ; the umbonal 

 ridge continuing to the post-basal extremity. 



