JURASSIC PERIOD. 165 



line very slightly oblique with the axis of the shell, the latter inclining 

 backward ; but yet more than half the bulk of the shell is in front of it ; 

 the margin of the lower two-thirds of the shell is regularly rounded, the 

 basal portion having rather a shorter curve than either the anterior or 

 posterior portions. 



Right valve apparently smooth, depressed-convex ; posterior ear rather 

 small, plain, its outer border forming a somewhat obtuse angle with the 

 cardinal border; anterior ear moderately large, prominent, proportionally 

 narrow ; byssal notch deep, narrow, the upper and lower sides approaching 

 each other at an acute angle ; anterior border extending farther forward 

 than the extremity of the anterior ear does ; the border at the front is 

 abruptly rounded and then continued backward and upward in an almost 

 direct line to the bottom of the byssal notch. Su.rface apparently marked 

 only by concentric strise of growth, but, in a favorable light, indications of 

 radiating strise may be observed upon the best-preserved examples. 



Height from base to beak, forty-one millimeters ; breadth, forty milli- 

 meters ; length of hinge, twenty-three millimeters. 



This shell resembles C. hellistriatus Meek and Hayden from Jurassic 

 strata of Dakota ; but it differs in the outlines of the borders, the shape of 

 the ears and of the byssal notch, and also in the surface-markings. 



Position and locality. — Strata of the Jurassic period ; east of Aquarius 

 Plateau, fifteen to twenty miles south of Dirty Devil River, and also at the 

 North Fork of Virgin River, Utah. 



Camptonectes bellistriatus Meek and Haydeu. 



Among the collections made at a locality of Jurassic strata, five miles 

 east of Gunnison, Utah, some imperfect examples of Camptonectes were col- 

 lected. They have the outlines and other characteristics, so far as they can 

 be observed, of C. hellistriatus Meek and Hayden, and probably belong to 

 that species. 



