304 GEOLOGICAL SURVEY OF THE TERRITORIES. 



minute and crowded between the beaks, which is as far forward as they 

 have been traced in the specimens examined. Surface showing very 

 fine, crowded, radiating striae, with stronger marks of growth. 



Length, 0.95 inch ; height, 0.37 inch ; convexity, 0.27 inch. 



This is not a typical Area, if we follow conchologists in viewing A. 

 Now as the type of the genus, because it wants the broad, divaricately- 

 furrowed cardinal area, and is not gaping in the anterior ventral region. 

 Its hinge denticles are also more oblique and longer posteriorly, more 

 like those of Scaphula. In form and general appearance it is very much 

 like some species of Macrodon, but its hinge characters are widely dif- 

 ferent. I know of no established section of the old genus Area into 

 which it could be properly placed, and if it is thought desirable to have 

 a section for such forms, they might be separated under the name 

 Arcina. 



Locality and position: Twelve miles southwest of Salina, Saline 

 County, Kansas ; Dakota Group of the Upper Missouri cretaceous series. 

 Professor B. F. Mudge. 



YOLDIA MICRODONTA, (MEEK.) 



Shell small, longitudinally subovate, rather compressed; anterior 

 margin more or less narrowly rounded, being generally more promi- 

 nent above the middle ; pallia! margin forming a semiovate curve, 

 being more prominent before than behind the middle, and curving up 

 gradually and obliquely at both ends ; posterior side compressed, and 

 with its" margin narrowly rounded, or almost subangular at its con- 

 nection with the hinge above ; cardinal margin sloping gradually from 

 the beaks, the posterior slope being very slightly concave in outline, 

 and the anterior nearly straight ; beaks rather depressed and placed 

 a little in advance of the middle; hiDge line equaling about three- 

 fourths the entire length, and provided with very fine, regular, pointed 

 denticles, of which twenty-six may be counted behind and twenty be- 

 fore the beaks, in each valve. Muscular and pallial impressions very 

 obscure, and not visible on internal casts. Surface not well known. 



Length, 0.50 inch ; height, 0.28 inch ; convexity, 0.14 inch. 



In general outline, and the nearly central positions of its beaks, this 

 shell bears some relation to Yoldia bisulcata, M. and W., from the Fox 

 Hills Group of the Upper Missouri cretaceous, but it is a very decidedly 

 more compressed species ; and, judging from impressions left in the ma- 

 trix, it was evidently less strongly striated. Indeed it seems to have 

 been nearly smooth, in which character, as well as in some other re- 

 spects, it is probably more nearly related to Y. LJvansi, M. and W., from 

 which it differs in being proportionally shorter, higher, and more com- 

 pressed. Among European species, it is represented by such forms as 

 Yoldia scapha (Nucula scapha, d'Orbigny, Palseont., Francaise, t. iii, PI. 

 301, Fig. 1-3), from which it also differs in being more compressed, with 

 the posterior side wider, and the posterior dorsal slope distinctly less 

 concave in outline. 



Locality and position : Twelve miles southwest of Salina, Kansas, from 

 a brown sandstone of the age of the Dakota Group of the Upper Mis- 

 souri cretaceous. Discovered by Professor Mudge, of the Kansas Agri- 

 cultural College. 



CORBICULA? NUCALIS, (MEEK.) 



Shell small, trigonoid-subcircular, moderately gibbous, the greatest 

 convexity being above the middle; pallial margin forming a semi-elliptic 



