108 PALAEONTOLOGY OF KENTUCKY. 



specimens the entire surface is ornamented by slender radiating, striae, which, 

 however, are not visible in most specimens. Concentric lamellose, imbricating 

 lines of growth are numerous in some specimens, while others show very few 

 or even none at all. 



Formation and Locality. Found rarely, and seldom well preserved, in the upper strata of the 

 Devonian limestone around the Falls of the Ohio, in Kentucky and Indiana. 



Spirifera arctisegmenta. HALL. 



Plate XII., figures 14 and 15. 



Spirifer arctisegmentus, Hall. Tenth Rep. on State Cab. 1867. 

 Spirifer arctisegmenta, Hall. Descript. of Hew Pal. Fossils, p. 91 1857. 

 Spirifer arctisegmenta, Hall. Pal. N. Y., Vol. IV., p. 208, pi. 81. 



Shell transversety semi-oval ; length equal or less than one-third of width ; 

 hinge-line equal to greatest width of shell, and terminating in salient angles 

 or mucronating points. Ventral valve the more convex; most convex at the 

 umbo, from which it slopes regularly to anterior and lateral margins ; mesial 

 sinus angular and distinctly defined quite to apex of shell ; beak not incurved ; 

 area flat and straight and a little inclined towards the front. The lateral view 

 given of this shell in figure 15, plate 12, is incorrect, by showing the area con- 

 cave and inclined towards the rear. Fissure narrow and open to apex. 



Dorsal valve depressed convex, scarcely flattened towards the cardinal ex- 

 tremities ; beak and central portion of the shell, together with the linear area, 

 slightly incurved. 



The surface is marked by from five to eight or nine angular plications on 

 each side of the fold or sinus, which on the ventral valve are slightly curved 

 towards the front, and of which only about three reach the beak, while the 

 balance run out along the margins of the cardinal area, where they coalesce 

 with an elevated ridge, which borders the area. The plications on the dorsal 

 valve are pretty direct ; fine, close, concentric, undulating striae mark the 

 entire surface. 



This shell may be distinguished from Sp. segmenta, as well as from other 

 allied forms, by its larger and more angular, as well as less numerous pli- 

 cations, and in having a distinct linear ridge along margin of area of ventral 

 valve ; its foramen is likewise narrower, and its sinus deeper and more angular 

 than in Spir. segmenta. (Hall.) 



Formation and Locality Found in the Corniferous limestone at and around the Falls of the Ohio 

 in Kentucky and Indiana, where it is, however, of rare occurrence, especially in well preserved speci- 



mens. 



