30 PALAEONTOLOGY OF CALIFORNIA. 



assistance of the description, and from the ff.ct that my specimens came from tho 

 original locality from which the first specimens were obtained, and this is the only 

 species with which I am acquainted that is found there, there is but little doubt 

 but that my reference of this form to Mr. Conrad's name, is correct. 



MYTILUS, L. 



M. MATHEWSONII, n. s. 



PI. 8, Fig. 51. 



SHELL very large, thick, curved, width and thickness ahout 

 equal in the centre, flatter towards the base; beaks terminal, 

 blunt. Surface marked only by lines of growth and irregular 

 concentric undulations. 



Figure, natural size. Some specimens have been found an inch or two longer. 



Locality and position : From the Miocene, south of Martinez, where it was found, 

 not rare, by Mr. Mathewson and Dr. Fish. 



Resembling M. Californiana in its unusually large size, it differs in being less 

 flabellate, more curved, more convex, and in having none of the radiating ribs 

 characteristic of that species. 



MODIOLA, Lam. 



M. MULTIRADIATA, n. 8. 

 PI. 8, Fig. 52. 



SHELL moderate in size, variable in form, more or less curved; 

 cardinal margin arched; posterior curved and descending more 

 or less abruptly; anterior margin sinuated, more or less deeply 

 excavated; beaks very small, subterminal. Surface marked by 

 numerous fine radiating lines except on the anterior fourth, which 

 is only marked by lines of growth. 



Figure, natural size. 



Localities and position : From the Miocene at San Emidio, west of Fort Tejon ; 

 and at Walnut Creek and Martinez, Contra Costa County. 



