28 PALEONTOLOGY OF CALIFORNIA. 



general curve as the rest of the shell ; ligament external. Hinge 

 composed of a single, long, sharp tooth, running from the beaks, 

 parallel with the cardinal margin, almost to the posterior end. 

 Pallial margin simple. 



This shell appears to belong to the family of Isocardiidas, presenting some ana- 

 logies to the genera Edmondia, Unicardium, and Cardiomorpha. 



C. DISJUNCTA, 11. S. 

 PI. 7, Fig. 48, 48 a, 48 b. 



Shell subquadrate; beaks terminal, anterior; anterior end 

 abruptly and angularly truncated; base broadly rounded; car- 

 dinal margin arched, sloping downwards towards the posterior 

 end. Surface marked only by lines of growth, except near the 

 posterior part where the peculiar truncation takes place, the 

 surface suddenly descending at a right angle to the curve of the 

 shell, for a short distance, and then resuming its former direction. 



Figures, natural size; 48 a, an outline from above ; 48 b, hinge. 



Locality: From Dead Man's Island, near San Pedro Bay; from a hard sand- 

 stone associated -with two or three previously known Tertiary Fossils. Probably 

 Miocene. 



I found a shell, abundant at Astoria, probably belonging to this genus. It was 

 described by Mr. Conrad in the Wilkes' Expedition Eeport, p. 724, pi. 17, fig. 10, 

 as Venus bisecta, and in the American Journal of Conchology, vol. 1, p. 153, as 

 Cyprina bisecta. 



LUCINA, Brug. 



Subgen. HERE, Gabb. 



Shell having all of the usual characters of Lucina, except that 

 the lunule is very deeply excavated, penetrating the hinge-plate, 

 and almost perforating it; bounded anteriorly by the anterior 

 lateral tooth, and posteriorly by the cardinal teeth. 



This form is very strongly characterized, and seems to form a well-marked 

 group in the genus. The following species exhibits the character more strongly 



