MOLLUSCA. 



CEPHALOPODA. 

 Genus Gomphoceras. 



Etymology : gomphos, a club; keras, a horn. 



Gomphoceras oviforme. HALL. 



Plate XXI., figures 17 and 18. 



Gomph. oviforme, Hall. Thirteenth Kep. N. Y. St. Cab., p. 1051860. 

 Oomph, oviforme, Hall. lilust. of Dev. Foss., Cephal., pi. 45 1876. 

 Cyrtoceras gibbosus, Hall. Illust. of Dev. Foss., Cephal., pi. 47 1876. 

 Oomph, oviforme, Hall. Pal. N. Y., Vol. 6, part 2, p. 3441879. 



Shell small, ovoid, sub-cylindrical, straight ; transverse section elliptical or 

 sub-circular ; longitudinal section sub-quadrate or sub-ovate. Plan of greatest 

 transverse section at the bottom of the body-chamber. The specimens of this 

 species found in our rocks have retained only a small section of the septate 

 portion of the shell ; usually only one or two septae are preserved. Apex is 

 truncated, apical angle about sixty degrees. Chamber of habitation compar- 

 atively large ; its length is about equal to three-fourths of its largest diameter ; 

 aperture large and trilobate (the one shown in figure 18, plate 21, is incorrect, 

 it is too narrow, and the third lobe, branching from the middle to the right, is 

 not at all illustrated, owing to the faulty condition of the shell which served 

 for illustration). Siphuncle near the ventral side, with a diameter of two mil- 

 limeters at the last septum. Test strong, having a thickness of one and a half 

 millimeters over the chamber of habitation. 



Our specimens do not show any surface-markings ; if any existed on perfect 

 and well-preserved individuals, they are obliterated on ours by the process of 

 silicification and by exfoliation. Our shells being internal casts, the suture - 

 lines are plainly shown. The specimen illustrated in figures 17 and 18, plate 

 21, is of average size of those here found. This species is easily distinguished 

 by its cylindrical form, and by the trilobate shape of its aperture. 



Formation and Locality. Found associated with its congener, Gomph. turbiniforme, in the chert 

 topping the hydraulic limestone of the Devonian formation, in Jefferson county, Ky., and Clark county, 

 Ind., where it is somewhat abundant, but not in fair specimen. 

 GKOI.. SUR. 25 



