CLINTON, LOAVER HELDERBERG, CHEMUNG, AND WAVEKLV GROUPS. 4.")1 



posterior margin obliquely truncate; cardinal line very slightly oblique, straight; 

 hinge line about two-thirds the length of the shell. 



Valves convex below the umbonal ridge, gibbous in the umbonal region; um- 

 bonal sIoj)e flat or a little concave. vmt.^ /-^W'^-^^^^^i:-^ 



Beaks at the anterior end, acute, incurved; umbonal '' ,k 



ridge very prominent, angular, extending from the beak to 



the basal extremity, curved. Along the middle of the pos- Atj i..^} 



teiior slope is a low rounded or subangular ridge, moderately conspicuous. 



Test marked by concentric stria?, which become fasciculate on that portion of the 

 shell below the umbonal ridge. The test is raised in a crest along the umbonal 

 lidgc. 



Anterior muscular impression situated at the anterior edge, ovate width two- 

 thirds the length ; pallial line near to and parallel with the basal margin, appearing 

 as a shallow groove on the casts ; posterior muscular impression not observed, 



A specimen of medium size has a length of 40 mm., and a height of 18 mm. 

 Other specimens preserve about the same pioportion. 



This species closely resembles Goniophora truncata of the Hamilton gi'oup, but 

 ■ the hinge line is much longer, and the posterior margin correspondingly less oblique. 

 From GoniopJioi-a chemungensis it is distinguished by its smaller size, more distinctly 

 curved umbonal ridge, and the ridge along the middle of the umbonal slope; from O. 

 jyerangtihi by the less angular form of the shell, the much less oblique posterior mar- 

 gin, and the ridge on the posterior slope ; from O. suhrecta by its much smaller size 

 and the ridge on the posterior slope, 



Fm'malion and locality. Chemung group, near Warren, "Warren county, Penn- 

 sylvania. 



NUCULA SINUOSA Simpson, n. sp., Fig. IS). 



Shell small, ovate cuneatc in outline, subnasute behind; height varying from 

 one-half to two-thirds the length, usually slightly more than one-half; anterior and 

 middle portions of the basal margins rounded, somewhat ab- va 

 ruptly constricted towards the posterior end ; posterior margin ' i 



obliquely truncate; anterior end abruptly rounded; cardinal \ 

 line, anterior to the beak, sharply declining ; more gradually 

 sloping to the iwsterior. A 



Valves slightly convex, greatest thickness of the shell a 

 slioit distance below tlie iitnlio. 



