452 NORTH AMERICAN INDEX FOSSILS. 



Triassic of Nevada ; California-British Columbia 

 243. P. curta Hall. (Fig. 594, b.) Jurassic. 



Surface marked with fine radiating plications, crossed by con- 



Fig. 597. Pseudomonotis equi striata. (Kan. Pal., VI/II.) 



centric striae, producing small nodes at points of intersection. 

 Sundance : South Dakota, Wyoming. 



LXXIV. Halobia Bronn. 

 Equivalve, semicircular to semioval, with straight hinge, and 

 almost central, scarcely prominent beaks. Teeth absent. Surface 

 radiately ribbed. Wings absent or represented anteriorly merely 

 by a smooth, non-projecting area. Triassic. 



Fig. 598. Pseudomonotis subcirculai-is, left valve. (Pal. Cal.) 



244. H. lommeli Wissmann. (Fig. 599.) Triassic. 



Beaks very small, abruptly pointed, turned slightly forward. 

 Surface marked with more or less wide and irregular flat ribs, 

 separated by linear furrows, and by a few concentric growth lines 

 near the beak. 



Nevada, British Columbia. 



