196 PALAEONTOLOGY OF CALIFORNIA. 



TRIGONIA, Brug. 



T. .^EQUICOSTATA, D. S. 

 (Indet. ; Pal. Cal., Vol. 1, pi. 26, fig. 198.) 



Shell small, trigonal, elongate; beaks prominent, anterior; 

 cardinal margin sloping posteriorly, straight to slightly convex 

 or concave ; anterior end regularly rounded ; base broadly 

 rounded, most prominent in the middle ; posterior end narrowly 

 truncated. Surface marked by regular, square, concentric ribs, 

 with equal, flat, interspaces ; these ribs end abruptly in advance, 

 and are continued by fine lines starting with an angle somewhat 

 less than a right angle ; posteriorly there is an angular ridge run- 

 ning from the beak to the posterior basal angle, and on crossing 

 this the ribs curve upwards towards the margin. Internally, the 

 surface is marked by four or five radiating ribs under the beak; 

 this character is not always present; the hinge teeth are unusu- 

 ally large, are coarsely ribbed, the anterior tooth being supported 

 longitudinally by a vertical plate, starting from the upper edge 

 of the muscular scar. 



Figure in Vol. 1, natural size. 



Common in the Chico Group at Orestimba Canon, Curry's, south of Mount 

 Diablo, Jacksonville, Oregon, and found occasionally at Martinez, and Cottonwood 

 Creek. 



AXIN^A, Poli. 

 A. sagittata, Gabb. 



(A (? Limopsis) sagittata, Gabb ; Pal. Cal., Vol. 1, p. 197, pi. 31, fig. 267.) 



At the time that this species was described, I was unable to decide finally as to 

 its generic relations. I have since been enabled to expose the area, which is very 

 narrow but characteristic, and which places it in the above genus. 



