208 PALEONTOLOGY OF KENTUCKY. 



versely elliptical. Valves ventricose, sometimes inflated ; beaks strong, prom- 

 inent and incurved ; hinge-line shorter than the shell, posterior to the beaks. 

 Dentition obscure, or represented only by irregular folds on the cardinal line ; 

 ligament external, prominent, extending from beneath the beaks to nearly 

 one-half the length of the hinge-line. Cardinal margin bordered by a small, 

 deep and strongly defined lunule. Anterior and posterior muscular impres- 

 sions faintly marked, the latter much the larger ; pallial line not sinuate but 

 broken into points or ridges, strongly rounded posteriorly, and uniting with 

 the large muscular scar near its anterior border. 



Surface of shell often marked by an oblique mesial rib or fold, extending 

 from the beak to the basal border, and by numerous strong, concentric folds or 

 ridges, which are frequently obsolete on the posterior part of the shell. The 

 shells appear to have been thin and fragile, and are usually much crushed and 

 distorted from compression. 



Grammysia gibbOSa. HALL AND WHITFIELD. 



Plate IV., figures 16 to 20. 



Qrammysia, secunda, var. gibbosa, H. and W. 24th Kep. on N. Y. St. Cabinet, p. 199 1872. 

 Qrammysia secunda, var. gibbosa, H. and W. 27th Rep. on N. Y. St. Cabinet, pi. 12 1875. 



Shell of medium size, sub-elliptical. Proportion of length and height vari- 

 able, but the length always less than twice the height ; basal margin gently 

 curved, with a distinct but shallow sinuosity anterior to the middle, this incur- 

 vation of the basal border is often very obscure, and in some specimens 

 entirely obsolete. Posterior extremity is strongly rounded. 



The cardinal line is straight, and measures about two-thirds of the length of 

 shell. Anterior end is short, and regularly rounded. Valves entirely equal, 

 moderately convex below and at the posterior end ; becoming gibbous in the 

 middle and above. Beaks almost anterior; of medium size and strongly in- 

 curved- and closely appressed. In some specimens the beaks of both valves 

 have different elevations above the hinge-line, one overlapping the other ; this 

 feature is not natural, but the result of some distortion. In perfect speci- 

 mens the beaks are of even height, and opposite to each other. The umbonal 

 slope is strongly rounded and extends to the posterior end of the basal margin. 

 A broad but very shallow depression extends from the beaks, crossing the 

 valves obliquely, and terminates at the basal sinus, forming a lateral sinus and 

 producing the basal one. In some specimens the lateral sinus is very obscure 

 and often entirely obsolete. The basal sinus is dependent upon the lateral 

 one; it is well marked, where the latter is plainly visible, and it becomes 

 obliterated, where the latter is obsolete. 



Surface of the shells, which occur only as internal casts, is marked by 



