CRETACEOUS FOSSILS. 175 



LUCINA, Brug. 



L. NASUTA, n. 8. 

 PL 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 siuuated 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 MartiSez ; collection of Mr. 

 Mathewson. 



L. POSTRADIATA, n. 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 



