202 PALAEONTOLOGY OF KENTUCKY. 



Cardinal line straight, oblique, having a length posterior to the beaks of 

 about one-half the length of the shell. Anterior end very short, curving 

 downward into the basal margin without limitation. Valves convex in the 

 lower and posterior portions ; gibbous in the middle and above. 



Beaks sub-anterior, small, distant, closely incurved, rising but little above 

 the hinge- line. Umbonal slope presenting an undefined ridge, which merges 

 into the general convexity of the shell about the middle of its length. Test 

 thick, marked by fine concentric striae, with distant imbricating lamellae. 



Ligamental area deeply excavated, marked by numerous longitudinal striae, 

 which are abruptly arched just beneath the beak. Hinge with two or more 

 cardinal teeth. Anterior muscular impression strong. 



Dimensions of the shells in this species do not vary much. Figure 16, plate 

 2, represents an individual of average size. 



This shell bears some resemblance, externally, to some species of Modio- 

 morpha and Nyassa, but its deeply grooved ligamental area is a distinctive 

 feature. Figure 18, plate 2, shows the said area of a left valve once enlarged. 



Formation and Locality. In the cherty layers of the Devonian limestone, which Prof. Hall places 

 among the Hamilton rocks, in Clark county, Ind., and in Jefferson county, Ky. It is found in well pre- 

 served, silicified specimens, but is a rather rare species ; it is represented in only a few collections in the 

 Falls Cities and elsewhere. Prof. Hall named this species in honor of the lamented Dr. James Knapp, ot 

 Louisville, Ky., who collected the first specimens of it, and loaned them to Erof. Hall for description and 

 illustration. 



Genus Conocardium. Bronn. 



Conocardium, Bronn. Lethaea Geognostica, Vol. I., p. 92 1835. 

 Etymology : konos, a cone ; kardia, the heart. 



Type : Cardium hybernicum, Sowerby. 



Shell equivalve, inequilateral, more or less fusiform or trigonal. Posterior 

 end obliquely truncate, produced along the cardinal line into a siphonal tube, 

 and sometimes the antero-inferior margin is also produced. Anterior end 

 conical and gaping in front. Beaks prominent and strongly incurved. Ven- 

 tral margins crenulated ; cardinal line straight ; umbonal ridge prominent, and 

 ornamented with an expansion of the test in continuation of the truncated 

 posterior end. 



Surface marked by concentric striae, and usually ornamented with strong 

 radii. Hinge with anterior and posterior laminar teeth. Ligament external ; 

 muscular impressions two in each valve, situated near the cardinal extremities ; 

 pallial line simple. In the anterior end there is a thickening or internal pro- 

 cess forming, apparently, a foot-sheath. 



