234 



NORTH AMERICAN INDEX FOSSILS. 



A. Shell with radiating striae I. 



I. Pedicle valve with a mesial sinus *. 



* Sinus very deep, giving the shell a bilobed appearance. 



134. C. verneuilianus. 



* Sinus with a mesial fold in it 132. C. mesolobus. 



* Sinus shadow and without mesial fold a. 



a. Shell about three fourths inch wide 131. C. granulifer. 



a. Shell smaller than above I. 



I. Hinge line forming greatest width of shell... 133. C. variolatus. 



1. Hinge line equal to or greater than greatest width of shell 



below 126. C. lepidus. 



I. Pedicle valve without a mesial sinus **. 



** Five to seven oblique spines on each side of the beak b. 



b. Shell large (about I inch wide) 2. 



2. Lateral striae curved anteriorly 118. C. jerseyensis. 



2. Lateral striae straight 122. C. coronatus. 



b. Shell small (about j4, inch wide) 3. 



3. Shell with 100-120 striae near front 129. C. illinoisensis. 



3. Shell with 50-60 striae near front 124. C. scitulus. 



** Two to four spines on each side of the beak (except 118 which may have 



more) c 



c. Spines vertical 125. C. setigerus. 



c. Spines oblique 4. 



4. Shell large (three fourths inch wide or more) f 



| Striae curving , 118. C. jerseyensis. 



| Striae not curving 119. C. hemispheric™. 



4. Shell of medium size (^ ± inch in general) ft* 



If Hinge line forming the greatest width of the shell aa. 



aa. Umbo of pedicle valve very abruptly incurved at the 



hinge line 123. C. pusillus. 



aa. Umbo of pedicle valve not abruptly incurved. 



128. C. logani. 

 ft Hinge line less than the greatest width of the shell 



below bb. 



bb. Striae uniform 121. C.vicinus. 



bb. Two central striae stronger than the others. 



126. C. lepidus. 



4. Shell small (about one fourth inch wide) ttt* 



fff Spines bending abruptly until parallel to the hinge line. 



120. C. mucronatus. 



fit Spines not bending abruptly 127. C. atirora. 



B. Shell smooth 130. C. glaber. 



118. C. jerseyensis Weller. (Fig. 284.) 



Siluric. 



Chonetes jerseyensis. (After Weller.) 



