572 PAIuEONTOLOGICAL REPORT OF GEOLOGICAL SURTET. 



rounded; hinge area straight; a little narower than the shell; height 

 •tVo °f an m °h; width .~\ of an inch; anterior ear .-j^-g- of an inch ; 

 posterior ear .—-j of an inch. 



It is easily distinguished from A. papyracea, Soiit., with which it has 

 been confounded, by the absence of a notch on the side, at the ex- 

 tremity of the anterior ear, and from the A. subpapyracea, De Ver.^ 

 with which it is more nearly related, by its less obliquity, straight an- 

 terolateral margin, wrinkles on the umbo, and simple ribs. 



Position and locality. It is most usually found converted into yel- 

 low pyrites, and in great abundance in the black shale forming the roof 

 of No. 9 coal, at the Kentucky Coal Company's and Curlew mines, 

 Union eounty, Kentucky, and in the equivalent beds of Gallatin coun- 

 ty, Illinois. 



A species, which we have not been able to distinguish from this, 

 occurs also, but not as abundant, in coal No. 11, at " Thompson's vein," 

 at Curlew mines, Union county, and at Bonharbour, Daviess county, 

 Kentucky. 



AVICULA A COSTA. Cox. 

 (PI. IX, fig 3; right valve natural size.) 



Small ; inequilateral ; very oblique ; sub-elliptical ; wings termina- 

 ting in small acute angles; anterior half as broad as the shell; pos- 

 terior very small ; surface and wings covered with fine concentric 

 striae; no ribs; height . T W of an inch; width .^% of an inch cardi- 

 nal border .-^\ of an inch. 



Position and locality. This small and fragile species" is found in 

 great abundance in the roof shales of No. 9 coal, in Union county, 

 Kentucky, and equivalent beds, Gallatin county, Illinois, and appears 

 to be characteristic of this vein, not having j et been found in any 

 other position. 



NAUTILUS DECOBATUS. Cox. 

 {PI. IX, fig. 4, profile natural size ; fig. 4 a, portion of the same showing, teptum and siphuncle; 



fig. 46, outline of the septu. 



Discoidal; whorls two and a half, not embracing, increasing in width 

 in the proportion of .-j%V to .—J^ of an inch; obtusely rounded on the 

 periphery; sides slightly convex; deeply plicated, forming elevated 

 ridges, one to each septa, and curved in the same direction; a depres- 

 sion in their centre produces two rows of small tubercles, more promi- 



