CRETACEOUS FOSSILS. 175 



LUCINA, Brug. 



L. NASUTA, n. 8. 

 PI. 24, Fig. 158. 



Shell small, very thin, subcompressed, inequilateral; beaks 

 small, acute, not prominent, placed a little behind the middle ; 

 anterior end broadly rounded and very prominent; posterior 

 cardinal margin straight, sloping downwards to unite with the 

 posterior end, which is narrow, produced, and subtruncate ; 

 basal margin convex, most prominent in advance of the mid- 

 dle, slightly sinuated posteriorly; umbonal ridge subangular, 

 straight. Surface polished, marked by faint, concentric lines of 

 growth, and by almost imperceptible radiating lines. 



Length, .55 inch. 



Locality : A single specimen, from Division A. , near Martinez ; collection of Mr. 

 Mathewson. 



L. POSTRADIATA, 11. S. 

 PL .24, Fig. 159. 



Shell very small, suboval, compressed, inequilateral ; beaks 

 small, moderately prominent, placed behind the middle ; hinge 

 margin excavated anteriorly, straight, and sloping downwards 

 posteriorly; anterior and basal margins regularly rounded, the 

 latter most prominent in advance of the middle ; posterior end 

 rounded, subtruncate; a sharp ridge passes from the beaks to 

 the posterior basal margin, behind which the surface falls sud- 

 denly as if dislocated, and then continues in a parallel plane with 

 the rest of the surface to the posterior margin. Surface orna- 

 mented by moderately large, regular, concentric ribs, and on the 

 posterior portion by two or three radiating ribs. 



Figure, three times the natural size. 



Locality: Division A., Texas Flat, Placer County; collection of the California 

 Academy of Natural Sciences ; collected by Dr. Trask. 



The peculiar character of the posterior end of this little fossil will at once 



