202 PALAEONTOLOGY OF CALIFORNIA. 



behind the middle, the anterior slope being broad and nearly flat ; 

 the entire surface covered by very numerous, slightly wavy, some- 

 what irregular, radiating ribs of small size, and with narrow inter- 

 spaces ; on the younger portion of the shell, the spaces between 

 the ribs are mere impressed lines, the ribs being convex ; near 

 the base, however, the ribs become proportionally smaller, the 

 spaces are wider than the ribs, and are concave, and the whole 

 are crossed by minute subsquamose lines of growth. 



Length from beak to base, of a broken specimen, 3 inches. 



From the vicinity of Lower Lake Village, Lake County ; from a deposit inter- 

 mediate between the Martinez and Tejon Groups. 



This shell belongs to the type of Sowerby's Plagiostoma, a group of extinct 

 species, well characterized by their peculiar surface ornament. I am familiar with 

 the external characters of a number of the species, but have never had the good 

 fortune of being able to examine the hinge. 



The present species is closely allied to L. microtis, nobis, but is proportionally 

 much broader, the posterior side is straighter, the anterior side is much more 

 regularly curved, being most prominent in the middle or below, while in microtis 

 the greatest prominence is just below the ear; the most marked difference seems 

 to be in the relative degree of obliquity of the two species. Another difference is 

 in the surface ornament ; both have numerous, small ribs, but microtis has the 

 interspaces punctate and the ribs flat, while the present shell has round ribs, and 

 the grooves are perfectly simple, except for the lines of growth. 



ANOMIA, Linn. 



A. Vancouverensis, n. s. 



PI. 33, Fig. 102. 



Shell circular, thin; upper valve unknown; lower valve flat; 

 marked by strong lines of growth and by very faint radiating 

 lines; aperture elongated, oblique, occupying nearly a third of 

 the diameter of the shell. 



Diameter, 1. inch. 



From the Chico Group, Departure Bay, near Nanaimo, Vancouver Island. 



It is not impossible that this may prove to be the under valve of A. lineata, nob. 

 (Vol. 1, p. 203, pi. 26, fig. 103), which belongs to the same group in the forma- 

 tion, and of which the lower valve was unknown. 



