404 



NORTH AMERICAN INDEX FOSSILS. 



Fig. 518. 

 obsolelus 

 VI.) 



Parallelodon IO5. 

 (Kan. Pal., 



end, the absence of a sharp constriction in the basal margin, and 

 in the presence of regular concentric varices. 

 Abundant in Hamilton : New York, Penn- 

 sylvania, Maryland, Ohio. Mississippic : 

 Ohio, Nevada. 



P. tenuistriatus Meek and Worthen. 

 Mississippic and Carbonic. 

 Strong radiating lines, scarcely visible ante- 

 riorly. Umbo large ; anterior end rounded ; length | inch. 



Waverly : Ohio. Coal Measures of Ohio-Nevada. 

 106. P. obsoletus Meek. (Fig. 518.) Mississippic-Carbonic. 



Base a little sinuate medially and nearly parallel with the hinge 

 line. 



St. Louis of Indiana. Coal Measures of West Virginia-Colorado. 



XXXII. Nemodon Conrad. 

 Equivalve, thin, small, transversely elongate, with sinuous base. 

 Beaks depressed and anterior to middle. Hinge area narrow, long 

 and nearly straight. Teeth consisting of a few minute granular 

 denticles directly under the beak ; lateral teeth few, long, linear, 

 parallel to the hinge margin. Laterals longer than in Cucullcea. 



Fig. 519- Nemodon brevifrons, with enlargement of cardinal region. (N. J. Pal., I.) 



Surface marked with very obscure, punctate, radiating striae and 

 concentric lines. 



Distinguished from Area and Parallelodon by its teeth. Cretacic. 

 107. N. vancouverensis Meek. Cretacic. 



Hinge and basal margins nearly parallel. Posterior end rather 

 squarely truncate and the two extremities nearly equal in breadth. 

 Length of small specimen | inch ; height \ inch. Surface marked 

 with numerous prominent radiating ribs. Umbo much larger and 

 more elevated than that of N. brevifrons. 



Horsetown : California, Oregon. Chico : California, Vancouver. 



