12 PALAEONTOLOGY OF CALIFORNIA. 



GENUS RHYNCHONELLA, Fischer. 

 RHYNCHONELLA (sp. undt.) 



SHELL small, subglobose, or subtrigonal. Dorsal valve more 

 convex than the other, most prominent a little in advance of the 

 middle, and rounding down to meet the other valve in front and 

 on each side ; ornamented with from nine to eleven simple, rather 

 obtuse, plications, which extend scarcely half way up towards the 

 beak from the front, three of them being raised anteriorly, so as 

 to form a moderately prominent mesial ridge. Ventral valve 

 somewhat compressed, most gibbous near the umbo; beak slightly 

 arched, and extending a little beyond, and closely pressed upon 

 that of the other valve ; surface with plications and mesial depres 

 sion corresponding with the mesial ridge and plications of the 

 dorsal valve; anterior margin provided with a mesial projection, 

 which fills a corresponding sinuosity in the front of the other valve 

 when the shell is closed. 



Length, 0.33 inch; breadth, 0.28 inch; convexity, 0.25 inch. 



In a genus like this, where there are so many closely allied species, it would be 

 folly to attempt to determine a species from a single imperfect specimen partly 

 embedded in the matrix, especially when it comes from a distant and hitherto 

 unexplored locality. I therefore merely give such characters and as good a figure 

 as the condition of the specimen will admit of,* and leave the determination of its 

 specific relations until we can have an opportunity to study better specimens. 



* This shell is not figured on the plates furnished by Mr. Meek. J. D. W. 



