TO JUNCTION OF GRAND AND GfiBEN RIVERS. 125 



rounded. Lower valve convex, the most gibbous part sometimes forming an obtuse 

 umbonal prominence, which is not separated from the front by a sulcus; beak slender, 

 pointed, and distinctly coiled to the left; surface ornamented by small, but distinct, 

 rather regular, radiating costse, which bifurcate along the umbonal ridge; marks of 

 growth rather obscure. Upper valve flat, oval, apparently smooth or only having ob- 

 scure lines of growth. 



Length from the most prominent part of the umbo to the ventral margin, 1 inch; 

 transverse breadth, 0.7*2 inch; depth or convexity, about 0.42 inch. 



It is possible that this shell may be identical with E.laviusculaoi Roemer(Kreid.vdn 

 Texas, plate ix, fig. 3 a, b, c); but with the means of comparison now within my reach, 

 1 can but regard it as distinct. All the specimens of it that I have yet seen are more 

 oval in form and have a less distinctly spiral beak than the form described by Roemer. 

 They also differ in having the under valve always marked by regular radiating costae, 

 while that of 11. leviuscula is generally quite smooth, or rarely presents traces of nearly 

 obsolete, lather broad, plications, as represented by tig. 3 c of Roomer's plate ix 

 (Kreid. von Texas). It seems likewise to be a thinner and less robust shell than 

 Ivoemer's species, and holds ;i lower stratigraphical position. In surface-markings as 

 well as in general form, it closely resembles young specimens of JE. columba of Lamarck 

 (Anim. sans Vert., vi, IDS) as figured by Goldfuss in his Petrefact. Germ, and by 

 d'Orbignv in the Paleont. Francais. It never attains more than one-eighth the size <>i' 

 adult individuals of that species, however, and differs in having an oval instead of a 

 circular upper valve. 



Locality and position. — Covero, Lower Cretaceous; also at Sierra Aba jo, from the 

 base of .Middle 1 Cretaceous, and at Gralisteo, from the same member of Dr. Newberry's 

 section. 



Genus ANOSMIA, Linn. 



Axomia NITJLDAj Mock. 

 Plate 1, figs. -1 «, /'• 



Upper valve Bubcircular or a little oval transversely, very thin and brilliantly 

 pearly, depressed-convex, the most prominent part being near the middle; lateral mar- 

 gins nearly equally rounded, ventral border forming a semi-oval curve; cardinal mar- 

 gin arched, or apparently presenting a similar outline to the ventral side; beak small, 

 much compressed, nearly or quite marginal, and located at the middle of the dorsal 

 side; surface marked by fine, rather regular, obscure, concentric stria". (Under valve 

 unknown.) 



Transverse; diameter, 1.07 inches; diameter from the cardinal to the ventral mar- 

 gin, 0.89 inch. 



It is possible that some of the species referred to the genus Anomia from the ( Jre- 

 taceous and older rocks would be found to present fundamental differences from the 

 typical forms of this group if we could see the under valve and the hinge and muscu- 

 lar impressions. Some six or seven species are now known from the Cretaceous rocks 

 of this country, of nearly all of which, I believe, only upper valves have been found. 



Locality and position. — Pope's Well ; top of Middle Cretaceous. 



