H. Doc. 129. 13 



much above the line of the base ; posterior margin and posterior basal 

 ' margin regularly rounded. 



Localities. Monterey ; Mission of San Diego ; Carmello. 



This interesting species is very abundant at Monterey, in indurated 

 drab-colored clay. There is merely a chalky trace of the shell re- 

 maining. It occurs in a somewhat similar rock at Carmello, and in 

 sandstone at San Diego. Figure 21 is from San Diego; 22 from 

 Monterey, and 23 from Carmello. 



23. T. PEDROA^A, (N. S.,) Con., pi. 2, fig. 17. Subtriangular, in- 

 equilateral, compressed ; anterior dorsal margin oblique, rectilinear ; 

 anterior extremity truncated, posterior margin regularly rounded, 

 basal margin subrectilinear. 



Locality. San Pedro. Kecent formation. 



A thin smooth species, of which only one valve was obtained. 



A RCA, Lin. 



24. A. MICRODONTA, Con., pi. 2, fig, 29. Rhomboidal, ventricose, 

 thick in substance ; anterior side very short ; umbonal slope rounded. 

 Bibs 25, prominent, narrow, wider posteriorly, except on the posterior 

 slope, where they are small and not prominent, about five in number. 

 Cardinal teeth small, numerous, closely arranged, larger towards the 

 extremities. Inner margin profoundly dentate ; dorsal area rather 

 wide and marked with about six impressed lines ; beaks distant. 



Locality. Tulare valley? Miocene. 



There is but one valve in the collection, and it has some resem- 

 blance to A. arata, Say, of the Maryland Miocene. The locality is 

 given by Mr. Blake with a mark of doubt. 



TAPES. 



25. T. DIVERSUM, Sow., pi. ii, fig. 24, 24a, and 26. Obtusely oval 

 or suborbiculary ventricose, inequilateral ; disk with numerous radiat- 

 ing prominent strise or ribs, and concentric wrinkled lines, which are 

 profound anteriorly ; posterior margin nearly direct, obtusely rounded 

 or subtruncated ; inner margin with small crenulations ; ligament 

 plate broad and profoundly indented. 



Locality. San Pedro, in calcareous marl. Eecent formation. 



SAX1CAVA, Fltur de Bell. 



26. s. ABRUPTA, Con., pi. ii, fig. 25 and 25. Suboval, ventricose, 

 inequilateral ; concentrically wrinkled ; anterior margin obtusely 

 rounded obliquely inwards ; posterior extremity truncated, direct, 

 dorsal and basal margin nearly parallel. 



Locality. San Pedro. Recent formation, 



PETRICOLA, Lam. 



27. P. PEDROANA, Con., pi. ii, fig. 23. Elliptical, profoundly ine- 

 quilateral, compressed, undulated concentrically, and with very minute 

 closely-arranged radiating lines. 



