1'22 PALAEONTOLOGY OF KENTUCKY. 



margins, vertical and extending to the cardinal extremities, where it does not 

 form an acute angle, but still maintains a visible height, which is not suffi- 

 ciently shown in figure 29, plate 10. Triangular fissure of moderate size. 



Dorsal valve very little convex, and flattened towards the cardinal extremi- 

 ties, and of equal size with the ventral valve. The mesial fold elevated, 

 rounded in the upper part, but somewhat flattened towards the front. 



Surface marked by about twelve prominent and rounded or sub -angular 

 plications on each side of the mesial fold and sinus, which are crossed by 

 strong, lamellose, imbricating, concentric striae and lines of growth, which give 

 the shell a rugose appearance. Only the plications next to fold and sinus 

 reach to the apex, the lateral ones run out along the margins of the area. 

 Length of shell about half of an inch and even less ; its width measures from 

 one inch to one inch and one-eighth. 



Prof. Hall has given in Pal. N. Y., vol 4, plate 31, subfigure 23, the ventral 

 valve of a shell which he calls, on page 206 of the same volume, Spirifera 

 varicosa, variety. His description is short and incomplete. His figure shows 

 some similarity with the present species, but it differs in its enlarged sinus 

 towards the front, and also by the area, which, in Hall's specimens, is partly 

 concave, while that of mine is always straight. 



Formation and Locality. Found in the upper strata of the Devonian limestone around the Falls 

 of the Ohio, in Kentucky and Indiana. It is rare, and seldom found in well preserved specimens. I 

 named this species after Orlando Hobbs, Esq., of JefFersonville, Ind., who is an ardent student and collector. 



Spirifera knappiana. N. sr. 



Plate VII., figure 14. 



Shell sub-circular, gibbous ; hinge-line shorter than width of shell ; cardinal 

 extremities rounded. 



Ventral valve gibbous in the upper part, and regularly curving to the front 

 and sides. Mesial sinus well defined from front to apex of beak, somewhat 

 shallow and rounded ; it contains two faintly marked plications. Beak of 

 medium size and curved over the area, which is high and concave, extending 

 over about two-thirds of the entire width of the shell ; fissure of medium 

 size. 



Dorsal valve gibbous, regularly convex on the sides, a little flattened at the 

 cardinal extremities ; mesial fold prominent and well defined to apex of beak, 

 containing on its middle a well marked depression ; beak small, slightly arched 

 over the sub-linear area, which is somewhat concave. 



Surface marked by from six to eight rounded plications on each side of 

 fold or sinus ; they are crossed by imbricating lines or striae, which have irreg- 

 ular distances in the upper part, but become regular and close set in the front 



