LAMELLIBRANCHIATA. 305 



Three specimens measure respectively 82, 57 and 50 mm. in length, and 

 32, 21 and 21 mm. in height. 



This species more nearly resembles G. carinatus, but the anterior end is pro- 

 portionally shorter, the sinus not so strongly marked, the post-cardinal slope 

 broader, and the striae not so abruptly recurved in passing the umbonal ridge. 

 From G. Chemungmsis it differs in its wider posterior end, the gentle downward 

 curving of the umbonal ridge, the wider cardinal slope and the less abrupt 

 recurving of the striae in passing the umbonal ridge. It is easily distinguished 

 from the last-mentioned species by these characteristics. 



Formation and localities. In the Chemung group, Franklin, Delaware county; 

 and at summit of hill, east of Charlottesville, and at Jefferson, Schoharie 

 county, N. Y. 



GONIOPHORA MINOR, n. Sp. 

 PLATE XLII, FIGS. 4-6. 



Shell small, trapezoidal ; length about one-third greater than the height ; basal 

 margin gently convex on the anterior half, becoming straight or slightly 

 arcuate behind ; posterior margin obliquely truncate. Cardinal line straight, 

 about two-thirds the length of the shell. Anterior end narrowly rounded 

 below the lunule. 



Valves convex below, becoming gibbous in the umbonal region. 



Beaks sub-anterior, closely incurved. Umbo prominent, angular. Umbo- 

 nal ridge sharply angular, continued to the post-basal extremity, and carry- 

 ing a conspicuous crest. Post-cardinal area slightly convex. 



Surface marked by strong, regular, concentric strias, which are less con- 

 spicuous on the post-cardinal area. One specimen shows indications of fine, 

 radiating striae on the posterior half of the valve. 



Anterior muscular impression strong, situated just within the anterior 



extremity. 



Two characteristic specimens have respective lengths of 12 and 11 mm., 

 and heights of 8 and 7 mm. A comparatively shorter form has a length of 

 9 mm., and a height of 7 mm. 



