TERTIARY FOSSILS. 15 



TROCHITA, Schum. 

 T. FILOSA, n. s. 



PI. 2, Fig. 25, 25 a. 



SHELL irregularly conical, variable in height and outline, some 

 times half as high as broad, sometimes height and width equal, 

 in outline sometimes circular, in other specimens very oblique; 

 volutions about two and a half; suture obsolete; internal plate 

 concave ; outer edge regularly rounded. Surface marked by nu 

 merous fine radiating lines, often dichotomous. 



Figures, natural size, from a very regular average specimen. 



Locality : From the Miocene of Walnut Creek, Contra Costa County. 



A single specimen was found with these, much higher than the average speci 

 mens, with a strongly marked spiral depression, and without the radiating lines 

 It will probably prove to be a distinct species, but in the absence of more mate 

 rial I do not feel warranted in naming it. 



PACHYPOMA, Gray. 



?P. BIANGULATA, n. S. 

 PI. 3, Fig. 26. 



SHELL large, conical; spire high; whorls five or more, sloping 

 above, flattened on the sides; suture small. Surface ornamented 

 by revolving rows of small tubercles; angles of the whorls 

 marked by a larger series than on the rest of the shell; under 

 surface nearly flat, marked by four or five revolving ribs with 

 marked flat interspaces. Aperture large, subquadrate ; outer lip 

 simple; inner lip and umbilical region unknown. 



Figure, natural size. 



Locality and position: A single, somewhat injured specimen, from the Miocene, 

 south of Martinez ; collected by Mr. Mathewson. 



Owing to the crystalline character of the shell, and the toughness of the matrix. 

 I have not been able to expose all of the important parts of the surface of this 



