CRETACEOUS FOSSILS 165 



M. NITIDA, 11. S. 

 PL 23, Figs. 145 and 14G. 



Shell moderate in size, inequilateral ; beaks small, prominent, 

 anterior, about a third of the length from the anterior end ; buc- 

 cal extremity deeply excavated under the beaks, prominently 

 convex below ; cardinal margin sloping convexly and rapidly 

 towards the anal extremity; basal margin broadly rounded. 

 Surface polished and marked by a few smooth, irregular lines of 

 growth. Lunule moderately large and bordered by a deep, im- 

 pressed line. 



Figures, natural size. 



Locality: Near Martinez, in loose blocks on the shores of the Straits of Car- 

 quines ; Orestimba Canon ; Chico and Cow Creeks (Division A.). 



This shell changes its shape materially in passing from the young to the adult. 

 The young form is shorter and proportionally more convex than is ever seen in 

 full-grown individuals. In general shape there is a great resemblance between 

 tbe present species and Venus varians (supra), but the smaller size, polished sur- 

 face, fewer and less distinct lines of growth, and the presence of the deeply im- 

 pressed line bordering the lunule will at once distinguish it. I am indebted to 

 Mr. Mathewson for the specimens described and figured. 



M. LONG A, U. S. 

 PI. 23, Fig. 147. 



Shell elongate, nearly equilateral; beaks small, broad, not 

 prominent; buccal ends broadly rounded, sloping inwards below 

 more rapidly than above; posterior end faintly subtruncated; 

 base broadly convex, most prominent below, or a little in advance 

 of the beaks. Surface marked by faint, irregular lines of growth, 

 and towards the beaks by minute, radiating lines, which become 

 obsolete as the shell increases in size. Lunule long, narrow, and 

 deeply impressed. 



Figure, natural size. 



Locality: From Division A., found in a mass of rock having the lithological 

 characters and the same grouping of species as is found at Texas Flat, Placer 

 County, but labelled "Shasta." From Dr. Behrens. 



