FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 199 



the rear wing is concave, but deflects back near the cardinal extremity, which 

 is angular. 



Test is of moderate thickness, and is ornamented by rounded, abruptly 

 elevated radii, with large, flat interspaces, which are sometimes occupied by 

 one and even two finer, radiating striae ; but in some shells these finer striae 

 are obsolete. These radii are crossed, and the large interspaces cancellated by 

 fine concentric lines of growth. Towards the margins, in the basal half of 

 the shell, the radii become either entirely obsolete, or at least very obscure. 

 On the wings the radiating striae are also obsolete, but .the concentric lines of 

 growth are there more prominent and crowded. On the anterior slope of the 

 left umbo exists a curved line of small and low nodules, numbering from ten 

 to twelve or more. This line starts at the beak and extends about an inch 

 towards the front. These nodes indicate small pits in the interior surface of 

 the shell, and served, probably, as attachment for some muscles. The right 

 valve has a similar line of nodes. The specimen here described measures three 

 inches in height, two inches and one-fourth in length, and its hinge-line one 

 and three-quarters inches long. 



Formation and Locality. Occurs in the cherty layers superimposed upon the hydraulic limestone 

 of the Devonian formation, in Jefferson county, Ky., and in Clark county, Ind., where it is found as a 

 silicifled internal cast. Not rare. 



Meek and Wortben. 

 Etymology : khno, I lean ; opisthe, backwards. 



Clinopistha SUbnaSUta. HALL AND WHITFIELD. 



Plate IV., figures 6, 7, 8 and 12. 



Tellinomya subnasuta, H. and W. 24th Reg. Rep., p. 1911872. 

 Dystactella (Tellinomya) subnasuta, H. and W. 27th Reg. Rep., pi. 21876. . 



Shell small, elongate, sub-elliptical, twice as long as high, with very ventri- 

 cose valves, giving the shell in its middle part a sub-cylindrical appearance ; 

 posterior end very narrow, shorter than the anterior one, and pointed at the 

 extremity ; anterior end regularly rounded, longest above the center ; basal 

 line in its central half almost straight, sometimes a little inflected opposite the 

 beaks, or slightly convex ; L its terminal parts turn in a gentle and regular 

 curve upwards to the anterior and posterior extremities ; beaks small and 

 closely appressed, situated at two-thirds of the length of shell from the an- 

 terior end. Muscular impressions of moderate size distinctly marked, situated 

 near the margin of valve ; pallial line entire, composed of a series of radiating 

 pustules, as seen on the cast. 



