554 Systematic Paleontology — Upper Devoxiax 



Leptostrophia interstrialis (Vanuxem) 

 Plate XLVIII, Pig. 7 



Strophomena interstrialis Vanuxem (non Phillips), 1S42, Geol. N. Y., Rept. 



3d Dist., p. 174, fig. 1. 

 Stropheodonta mucronata Hall (non Conrad), 1867, Pal. N. Y., vol. iv, p. Ill, 



pi. XV, figs. 13, 14. 

 Stropheodonta interstrialis Schuchert, 1897, Bull. U. S. Geol. Survey, No. 



87, p. 423. 



Description. — " Shell semioval, the proportions of length and breadth 

 varying considerably, the hinge-line often extended beyond the width of 

 the shell. The ventral valve is very depressed-convex, and the dorsal 

 valve nearly flat. The area of the ventral valve is extremely narrow, and 

 the inner margin crenulated for about half its length. The surface is 

 marked by distant sharp elevated striae, with the interspaces occupied by 

 numerous finer undulating striae. The muscular impressions are faintly 

 marked; those of the oeclusor muscles occupy a minute space near the 

 apex of the cast; and the divaricator muscular impressions are elongate 

 and spreading, and partially limited by an oblique pustulose ridge on 

 each side, in form and character like those in S. perplarm, but less 

 strongly defined. The cardinal process of the dorsal valve is slender, and 

 supported at its base by an oblique ridge on each side, between which the 

 muscular markings are faintly impressed." Hall, 18GT. 



Length 15 mm.; width 22 mm. 



The individuals observed are smaller than those figured by Hall, their 

 coarser striae are also somewhat nodose while the finer striae are slightly 

 undulating. They resemble L. perplana var. aUernaia from which they 

 differ in smaller size and in having straighter and less nodose striiB. They 

 occur also at a lower horizon. The resemblance to L. perplana var. alter- 

 nata is so close in some cases, however, that the separation of this variety 

 from that species is not fully assured. 



Occwrence. — Jennings Formation, Woodmont Member, Ithaca 

 Fauna. Hancock-Harrisonville Road, 880; Millstone, 795. 



Collection. — Maryland Geological Survey. 



