PAL.EONTOLOGICAL REPORT OF GEOLOGICAL SURVEY. 571 



greatest depth at the umbo; beak small, acute, elevated above and 

 gradually sloping, with a slight depression to the sides ; entering valve 

 remarkably ventricose, and a little longer than the receiving valve ; 

 greatest depth at the disk; a very obscure shallow sinus is perceptible, 

 running from the rostrum to the disk, where it is lost or obliterated by 

 the crushed condition of the base of the shell ; surface ornamented 

 with five or six broken spines, two lines in diameter and about the 

 same height, and sevei al scars of missiug spines ; beak very tumid, 

 acutely terminated, slightly incurved, moderately arched on the car- 

 dinal margin; sides obtusely rounded, broad and distinctly marked 

 by rugose fimbriating lines of increment; width l. T W inches; length 

 .l. T W inches; hinge line l.^V inches; depth of receiving valve 

 .y 3 ^ inch ; depth of entering valve .y^ ; width of cardinal area .J— 

 inch; depth .-j%^- inch. 



Though several authors have suggested the appearance of scars left 

 by spines, on some species of orthis ; this is believed to he the first 

 specimen of the genus upon which they have actually been found 

 attached. 



The great convexity of the entering valve, the obtuseness of both 

 valves at their lateral border, and the greater prolongation of the en- 

 tering valve, distinguishes this species from the 0. resupinat'a, (Mart, 

 sp.,) to which it is most nearly related. 



Position and locality. From the siliceous micaceous shale forming 

 the roof of the upper coal, No. 11, at Mr. Hawes' mine, Hawesville, 

 Hancock county, Kentucky. 



AVICULA RECTA-LATERAREA Cox. 



(PI. IX, fig. 2, right valve natural size.) 



A little higher than broad; inequilateral; slightly oblique; covered 

 with numerous radiating ribs, increasing in number by the intercala- 

 tion of new ones, occasionally by dichotomy; nearly as high as broad; 

 a little wider than the space which separates them from one another; 

 anterior ear extends to the lateral border, with which it nearly forms a 

 right angle ; posterior ear a little shortpr than the anterior, is not ter- 

 minated by an angle, but by a rounded and well defined by a notch at its 

 base; umbo slightly, tumid, crossed by irregular concentric wrinkles; 

 surface and ears covered with fine striae, and fimbriating lines of in- 

 prenjeat ; , ajitjerior side „ rectalineal ; base afld posterior s^tle, ^obtusely 



