156 PALAEONTOLOGY OF CALIFORNIA. 



convex, most prominent anteriorly, and sloping upwards to the 

 posterior end nearly straight; shell a little more than twice as 

 long as wide. Surface marked by numerous microscopic, con- 

 centric lines, generally somewhat irregular. Muscular scars 

 deep ; pallial sinus broad, shallow. 



Figure, natural size. 



Localities: In Division B., near Martinez; and abundant at Marsh's, fifteen 

 miles east of Mount Diablo. A single specimen was found at Alizos Creek, near 

 Fort Tejon. 



T. Remondii, n. s. 



PI. 22, Fig. 132. 



Shell broad, thin, compressed, about a third longer than 

 wide ; anterior end broadly rounded ; posterior rostrate, nar- 

 row, and truncated obliquely outwards and downwards; beaks 

 small, central, prominent; base broadly rounded, slightly sinu- 

 ous near the posterior extremity; a well-marked ridge passes 

 from the beak to the posterior basal, angle ; cardinal margin 

 convex in front, concave behind the beaks, and sloping down- 

 wards concavely towards the truncated posterior end. Surface 

 ornamented by numerous small, regular, concentric ribs, and by 

 smaller, radiating, interstitial lines. 



Figure, natural size. 



Locality : Two specimens from Cochran's, sis miles east of Mount Diablo, col- 

 lection of Mr. R6mond; one from near Fort Tejon. 



T. HOFFMAJOTIANA, 11. S. 

 PL 22, Fig. 133, and 133 a. 



Shell moderate in size, compressed, a little longer than wide; 

 beaks nearly central, somewhat variable, prominent; cardinal 

 margin sloping each way, nearly straight, most abrupt poste- 

 riorly ; anterior end broadly rounded, posterior produced, nar- 

 row, rounded or sub truncate, and sometimes slightly reflected 

 laterally ; basal margin convex, most prominent directly under 



