20 PALEONTOLOGY OF THE EUKEKA DISTEICT. 



Kutorgina sculptilis Meek (Sp). 

 Plate i, figs. 7, 7 a, 6; pi. ix, fig. 7. 



Iphidea (f f ) sculptilis Meek, 1873. Sixth Ann. Eep. U. S. Geol. Surv. Terr, for the year 



1872, p. 479. 

 Kutorgina minutissima Hall & Whitfield, 1877. U. S. Geol. Expl. Fortieth Par., 



vol. iv, p. 207, pi. i, figs. 11, 12. 



Shell minute, semicircular to subquadrangular; hinge line usually a 

 little shorter than the greatest width of the shell; sides slightly rounded; 

 antero-lateral angles rounded; frontal .margin gently convex or nearly 

 straight along the middle. 



Ventral valve obliquely depressed, subconical, with the somewhat ob- 

 tusely pointed apex on, or slightly extending over, the cardinal line; area 

 vertical or bending a little backward, triangular; width a little more than 

 twice the height, but not as broad as the shell, owing to the sides of the latter 

 curving in to meet the straight area at an angle of about 50 ; foramen (?) 

 large, dorsal valve depressed convex, most elevated on the umbo; beak a 

 little depressed, scarcely projecting beyond the cardinal line; mesial sinus 

 faintly defined, not much more than a slight flattening in many examples; 

 area low, general characters unknown. 



Surface of the shell marked by very fine, sharp, elevated, concentric 

 lines, that coalesce or bifurcate irregularly, giving a peculiar, interrupted, 

 wavy appearance under the magnifier; these lines extend around on the 

 sides of the posterior side or area to the edges of the triangular foraminal- 

 like opening. Slightly irregular, slender, depressed or elevated interrupted 

 lines radiate from the beak or apex; they vary in strength and number, and 

 on some shells are scarcely discernible, although forming a prominent feature 

 in many individuals. 



Length of largest shell observed, 2.5 mm ; breadth, 3.75 mm ; depth of ven- 

 tral valve, 1.25 mm ; of dorsal valve, 0.5*. 



The type of Iphidea (??) sculptilis (Meek) is a strongly marked ventral 

 valve of this species from the east side of the Gallatin River, Montana, where 

 it is associated with Acrotreta gemma Billings, and Ptychoparia Oweni Meek. 



