56 BEAOHIOPODS. 



as pointed out in the remarks accompanying the description of 

 Ch. lavis, hold good throughout the entire series collected. As 

 some of the specimens of the smooth species often show faint 

 radiating striae, it has been suggested that these shells are 

 merely water-worn individuals of other forms. This, however, 

 does not appear to be the case, as a large number of both 

 species have been found intimately associated; and in Ch. 

 mesoloba the radiating stride are very sharply defined and well 

 preserved. Besides, the conditions under which the mollusks 

 of these species flourished show conclusively that all influences 

 of wave action were absent during the deposition of the 

 deposits. 



Chonetes granulifera OWEN. 



Chonetes granulifera Owen, 1852 : Geol. Sur. Wisconsin, Iowa and Min- 

 nesota, p. 583, tab. v, figs. 12a-c. 

 Chonetes granulifera Norwood <fc Pratten, 1854: Jour. Acad. Nat. Sci., 



Phila., vol. Ill, p. 24. 

 Chonetes smithii Norwood & Pratten, 1854 : Jour. Acad. Nat. Sci., Phila., 



vol. Ill, p. 24, pi. ii, figs. 2a-c. 

 Chonetes mucronata Meek & Hayden, 1858: Proc. Acad. Nat. Sci., Phila., 



p . 262 . ( N ot Conrad , 1843 . ) 

 Chonetes mucronata Meek & Hayden, 1864: Pal. Upper Missouri, p. 22, pi. 



i, figs. 5a-e. 

 Chonetes mucronata Geinitz, 1866 : Garb, und Dyas in Nebraska, p. 58, 



tab. iv, figs. 12, 13, 14. 

 Chonetes granulifera Meek, 1872: U. S. Geol. Sur. Nebraska, p. 170, pi. 



iv, fig. 9, pi. vi, fig. 10; pi. viii, fig. 7. 

 Chonetes granulifera White, 1875 : Expl. and Sur. w. 100 Merid , vol. IV, 



pt. ii, p. 122, pi. ix, figs. 8a.-c. 



Shell rather large, semicircular ; hinge-line longer than 

 greatest breadth of shell anteriorly. Ventral valve regularly 

 convex, with the mesial sinus broad yet shallow ; beak small, 

 extending but slightly over the hinge area ; cardinal margig 

 provided with from seven to ten spines on each side of 

 the beak. Area narrow, with a wide foramen which is par- 

 tially covered by a pseudo-deltidium. Hinge teeth well de- 

 fined, narrow, finely lined. Dorsal valve concave, rather 

 closely appressed against the opposite valve. Surface of shell 

 marked by numerous fine, radiating ribs, with a few concentric 

 lines of growth which are usually more or less imbricated. 



