60 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



margins nearly straight, meeting in almost a right angle ; luniile 

 distinct, bordered by an impressed line and marked with fine 

 concentric striations; escutcheon large, lanceolate, sloping in- 

 ward, the lamellse stopping abruptly at its outer margin; sur- 

 face ornamented with five or six very prominent reflexed con- 

 centric lamellae, numerous fine concentric lines of growth, and 

 fine radial striations which are hardly visible on some speci- 

 mens; the concentric lamellae are wavy and thin on the mar- 

 gins but thick at the base ; hinge line angulated, with three car- 

 dinal teeth in each valve, the middle one usually bifid. 



Dimensions: — Length of the type specimen, 15 mm.; alti- 

 tude, 8 mm. ; thickness of a single valve, 4.5 mm. 



Occurrence : — Not uncommon in the middle portion of the 

 lower Miocene of Kern River, California, locality 65. 



Type:— No. 118, and cotypes Nos. 119 and 120, Cal. Acad. 

 Sci., on west bank of a small canyon IVi miles northeast of 

 Barker's ranch house, Kern County, California. Coll., Bruce 

 Martin. 



Genus TRANSENNELLA Dall 



Transennella joaquinensis, new species 



Plate 3, figures 6a, 6b and 6c 



Shell small, solid, circular in outline; valves equal, inequi- 

 lateral, convex ; beaks elevated, turned forward a little anterior 

 to the middle ; umbones full ; dorsal margin concave in front of 

 the beaks, nearly straight behind; extremities well rounded; 

 base arcuate; surface marked with numerous fine concentric 

 lines ; lunule cordate, bordered by an impressed line ; hinge plate 

 of the left valve with three cardinal teeth and one anterior 

 lateral which is elongated diagonally; the middle cardinal not 

 distinctly bifid ; pallial sinus small and shallow. 



Dimensions : — Length of the type specimen, 8 mm. ; altitude, 

 7.5 mm. ; thickness of the right valve, 2.5 mm. 



Occurrence : — Not uncommon in the lower Miocene of Kern 

 River, California, locality 65. 



This species can be separated from Transennella tantilla 

 Gould and T. calif ornica Arnold, by its less elongated form, 

 more elevated beaks, and more prominent umbones. 



