192 PALAEONTOLOGY OF CALIFORNIA. 



f 



rounded and produced; cardinal margin slightly arched; base 

 concave in the middle, convex posteriorly ; posterior end irregu- 

 larly convex, most prominent below. Surface marked by coarse, 

 irregular lines of growth. 



Length, 4.8 inches; width, 2.4 inches; diameter about 1.5 inch. 



Common in the white limestone of the Shasta Group, east of Knoxville, Lake 

 County ; also found smaller in the same beds in Morgan Valley, south of Clear 

 Lake, and at the Hot Sulphur Springs, east of Clear Lake, Colusa County. 



A fine species, well characterized by its size, being the largest species of the 

 genus, with which I am acquainted. Some specimens are over six inches in 

 length. 



MELEAGRINA, Lam. 



M. ANTIQUA, 1). 8. 

 PL 81, Fig. 89. 



Shell small, flattened, rounded quadrate; beaks acute, pro- 

 duced, and terminal; cardinal margin straight, very slightly slop- 

 ing; anterior margin strongly sinuous for a short distance under 

 the beaks, continued in a regular curve, running into the base, 

 which is a little the most prominent posteriorly; posterior mar- 

 gin nearly straight, uniting with the base by a more abrupt curve 

 than that on the anterior side. Surface plain, or marked only by 

 lines of growth. Hinge slender; muscular scar large, broadly 

 reniform, placed a very little posterior to the middle. 



Length, 1.3 inch ; width, 1.5 inch ; thickness of two valves, .32 inch. 



From Departure Bay, Nanaimo, Vancouver Island, associated with Trigonia 

 Evansana, Pecten Traskii, and other fossils equally characteristic of the Chico 

 Group. 



The oldest known species of the genus, being from a deposit certainly older than 

 the white chalk. It possesses all of the generic characters in a much more marked 

 manner than we might feel warranted in expecting, when we consider how far 

 removed the species is from the geological ago in which the genus has obtained its 

 greatest specific development. It is usually the case that, where a genus attains 

 its greatest numerical specific development in any one geological age, those species 

 which first appear, especially if in a remote formation, as well as those that mark 



