— 51 — 



Waldheimia imbricata n. sp. (PL IV, Figs. 50, 51.) 



Lower valve subquadrate, moderately convex, a little more prominent 

 at middle; basal margin nearly straight; about thirty low ribs diverg- 

 ing from apex; crossed beyond the middle by six or seven concentric 

 furrows, marking stages of growth, and giving an imbricated appear- 

 ance. Lateral margins at right angles to anterior, and nearly straight; 

 posterior margin gently rounded, and slightly undulated by the median 

 furrow. Upper valve more convex; ribs fewer and stronger, the median 

 six or seven ribs depressed. Length of base, 0.90; of shell, 1.00 inch; 

 height, 0.50; diameter, 0.50. 



The same remarks given with the last apply to this, but it looks 

 very much like some Waklheimias now living on the coast. It was 

 found only at La Jolla, by Mr. Fairbanks. At that place a Quaternary 

 raised beach, of materials similar to those of the Cretaceous beds, again 

 encroaches on the latter, containing Donax californicus, etc., and the 

 two formations can only be separated by the species of fossils found in 

 them, as far as lithological, if not stratigraphical, characters go. The 

 fossils of Cret. B are, however, mostly absent, and Ammonites are found 

 there. 



II. TERTIARY-MIOOENB, AND PLIOCENE. 

 A. FROM KERN COUNTY. 



Mr. "Watts collected a large number of specimens in this county, 

 many of which Avere identified with species still living on the coast; 

 others, with supposed extinct species, already described as fossils, and 

 several appeared to be new. So many Tertiary species are, however, 

 known to still exist on the coasts of Lower California, and to have been 

 described from the living shells, that it is not considered advisable to 

 describe the fossils until they have been comi:)ared with the living 

 species from the south, which are imperfectly known, and besides this 

 the fossils were usually in poor condition, A few are excepted, which 

 have before been imperfectly figured, and some described by Conrad. 

 The reasons are given under each species described or figured. There 

 are also two species of Pinna, of which descriptions were first published 

 in the Catalogue of Fossils, 1888. 



B. FROM SAN DIEGO COUNTY. 



The " mesa," or table land, which rises gradually with a gentle slope 

 from San Diego Bay for eight miles northeast, and is then suddenly 

 uplifted by recent volcanic action, its eastern edge resting against 

 igneous rocks, contains abundant fossils, but in such a poor state of 

 preservation where exposed, that it is usually impossible to do more 



