FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 159 



spreading, broadly sinuate in front, and sometimes with a deep notch in the 

 middle. The margin gently recurved, joining the volution a little on the 

 ventral side where it is thickened, somewhat abruptly curving over and partly 

 inclosing the small umbilicus, and extending in a callus over the columellar 

 lip, which is sometimes distinctly striato-pustulose. 



Surface marked by strong longitudinal or revolving striae, which alternate 

 in size ; are sometimes fasciculate, and often finer and more numerous on each 

 side of the dorsal band than on the lateral portions of the shell. The revolv 

 ing striae are cancellated by finer, sub-equal, thread-like, transverse striae. 

 The dorsal band is narrow, rarely elevated, or sometimes scarcely raised above 

 the surface, and usually flat or slightly concave ; the concentric striae making 

 an abrupt retrorse curve upon it in crossing. The band is likewise usually 

 marked by two, three or more revolving striae, finer than those on the sides of 

 the shell, and sometimes quite obscure. 



This species is very variable in size and form as well as in surface-markings, 

 which are, however, mainly due to the distortion of the shell. A specimen 

 without distortion is a very rare occurrence. The average size of this shell is 

 about three-fourths of an inch. The specimens found in our rocks seldom 

 exceed the one illustrated on our plate. 



Formation and Locality. Occurs in the rotten hornstone of the upper strata of the Devonian for- 

 mation, in Jefferson county, Ky , and in Clark county, Ind., where it is not rare, but fair specimens are 

 seldom found. 



Genus Bucania. Han. 



Bucania, Hall Pal N. Y., Vol. 1-4847. 

 Etymology . bukane, a trumpet. 



Shells convolute ; spire equally concave on either side ; volutions in the same 

 plane, all visible, outer one ventricose, inner ones usually angulated on the 

 edge, concave on the ventral side ; aperture rounded oval, somewhat com- 

 pressed on the inner side by contact with the next volution, laterally and dor- 

 sally abruptly expanded. 



This genus is established for the reception of several species of shells of a 

 peculiar form, which were formerly placed with the Bellerophons, but from 

 which they differ by having all their volutions visible, which is not the case in 

 Bellerophon proper. Bucania differs from Porcella in being symmetrical, the 

 volutions in the same axis being equally expanded on either side, both sides 

 presenting the same aspect, and the aperture corresponding to the axis of the 

 shell. 



