28 PALAEONTOLOGY OF CALIFORNIA. 



MYACITES. Schlot. 

 M. (PANOPCEA ?) HUMBOLDTENSIS, n. s. 



PL 5, Fig. 22. 



SHELL equivalve (?), inequilateral ; beak between a third and a, 

 fourth the length from the buccal end. Cardinal margin slightly 

 elevated ; posterior extremity broader than the anterior, and a 

 little more regularly rounded. Surface marked by a few regular, 

 prominent, rounded, concentric ribs. Length, 1.05 inch. Width 

 from beak to base, .55 inch. Depth of valve, .1 inch. 



This shell has only been found as internal casts. I refer it to Schlotheim's 

 genus, Myacites, on the same grounds on which he founded the genus, the external 

 form. Later authors appear to doubt the validity of the genus. Be that as it 

 may, it is very probable that among the antique forms, referred to the genus 

 Panopcea, and of which the hinges have not been discovered, we may find not only 

 one, but several distinct generic divisions. 



Collected by G-. Blake, in the Buena Yista District, Humboldt Mining Eegion, 

 Nevada Territory. 



PANOPCEA, Menard de la Groye. 

 ? P. KEMONDII, n. s. 



* 



PI. 5, Fig. 23. 



SHELL subelliptical, oblique, thin; beaks subcentral, promi 

 nent; anterior end rounded; posterior sometimes produced, some 

 times regular ; most prominent towards the base. Surface marked 

 by concentric undulations and fine lines. 



Figure, natural size. 



Locality: From San Marcial, Sonora, Mexico. Collected by Mr. Esmond. 

 Associated with two or three other bivalves, one apparently a Cardium, too im 

 perfect for description. In the same formation were found fragments of fossil 

 plants, probably Triassic. 



