56 PALAEONTOLOGY OF KENTUCKY. 



there are several times as many at the margins as at their starting. On most 

 specimens the central plications form in their basal half, by double bifurcation, 

 fascicles or bundles of ribs, such as mark so prominently the surface of Spir. 

 camerata of the Carboniferous. These fascicles are only found on the middle 

 lobe of the shell; the lateral lobes contain only single and much finer plica- 

 tions. The sides of the shell, along the cardinal line, and down to the point 

 of maximum width of the shell, have a smooth surface. 



Concentric lines of growth cover the shell. This species resembles some- 

 what Mr. Billings' Stricklandinia gaspensis, from which it differs by not 

 having any mesial depression or elevation, and no straight hinge-extension 

 and narrow area ; while Mr. Billings' shell is covered, even on the sides, by 

 plications, where P. knappi has a large, smooth lateral area. 



Prof. Hall says that this shell resembles, in every feature except the strongly 

 radiated surface, Pentamerus oblongus, and he does not doubt the possibility 

 that intermediate forms may be found to connect the two species. It can not 

 be disputed that this shell greatly resembles some of the broader forms of Pent, 

 oblongus, from which it certainly branched off by evolution, and I feel certain 

 that it will maintain its specific character. 



Formation and Locality. Found in the Niagara rocks in, the quarries east of the city of Louisville, 

 Ky., where it is not very rare, at least not in fractional shells; while perfect individuals are exceedingly 

 seldom. Prof. Hall named this species in honor of the late Dr. James Knapp, of Louisville, Ky., who first 

 discovered it, as he did so many other new species, belonging to the palseozoic fauna of Louisville's vicinity. 

 Dr. Knapp was, for many years, almost the only collector of fossils of our city, thus having the rare 

 opportunity of getting all the line specimens which our many quarries around the city and the Falls ot 

 the Ohio afforded. 



Pentamerus knotti. x. SP. 



Plate XXXII., figures 9, 10, 11 and 12. 



Shell below medium size ; broadly ovate, sub-globose ; length and width 

 about equal ; hinge-line shorter than the greatest width of the shell ; cardinal 

 extremities rounded ; lateral and basal margins forming usually a regular 

 curve, but sometimes the front is slightly straighter than the sides. Shell 

 very gibbous and surface plicated. Ventral valve more gibbous than the 

 other, having its greatest convexity about the middle of the valve, from where 

 it curves regularly to the lateral and basal margins, but very abruptly to the 

 cardinal area, with which it joins without any line of demarcation ; about the 

 middle of the valve, or, at least, below the umbo, the central portion for the 

 extent of four plications becomes elevated above the adjacent surface, slightly 

 increasing in height towards the front, thus forming a mesial elevation or fold ; 

 the umbo is prominent, and the beak elevated and strongly incurved, but not 

 overlapping the umbo of the dorsal valve ; the cardinal area is not defined in 



