30o 



NORTH AMERICAN INDEX FOSSILS. 



the middle through a broad, undefined sinus; beak not incurved. 

 Surface smooth or with faint concentric growth lines. 



Oriskany-Onondaga of New York, Kentucky, Indiana, Michigan, 

 Ontario. 



289. C. impressa Hall. (Fig. 372, d-e.) Devonic. 

 Pedicle valve angularly convex. Brachial valve small with front 



produced and curved downward to fill the sinuosity in the front of 

 the pedicle valve. Surface covered with fine concentric and faint 

 radiating striae. 



Hamilton of New York. 



LXXXVI1I. RensseljEria Hall. 

 Oval or suborbicular, usually gibbous. Beak of pedicle valve 

 prominent, acute and incurved. Valves without mesial fold or 

 sinus. Brachial valve with large hinge plate; brachidium form- 

 ing a broad plate anteriorly and giving off two small, rod-like 

 processes posteriorly. Surface radially striated or finely plicated. 

 Shell structure punctate. Devonic. 



290. R. aequiradiata (Conrad). Devonic. 

 Elliptical, with nearly equal valves. Pedicle valve often sub- 

 angular along the center toward the umbo, with beak incurving 

 over that of the opposite valve. Surface marked by simple radi- 

 ating striae, which are most conspicuous near the margin. 



Helderbergian of New York, Nova Scotia. 



Fig. 373. Renssekeria ovoides (Pal. N. Y. , III.). 



291. R. ovoides (Eaton). (Fig. 373.) Devonic. 



Length usually much exceeding the breadth, broadest above the 



