168 PALAEONTOLOGY OF KENTUCKY. 



Platyceras thetis. HALL. 



Platyceras thetis, Hall. Desc. of New Foss., page 41861. 



Platyceras thetis, Hall. 15th Kegent's Rep., p. 321862. 



Platyceras thelis, Hall. Illust. of Dev. Foss., pi. 31876. 



Platyceras thetis, Hall. Pal. N. Y., Vol. 5, pt. 2, p. 81885. 



Shell oblique arcuate from base, with the apex incurved, nucleus making 

 barely more than a single minute volution ; gradually expanding from the 

 apex to near aperture, which is sometimes more abruptly spreading. The 

 beak of the body- whorl is prominent, and a little flattened on the left side, 

 while right side, from one-third to one-half the length, is sometimes marked 

 by two or three longitudinal folds, and often by more numerous, finer plica- 

 tions. Aperture a little oblique, nearly round or sub-quadrate, with the peris- 

 tome sinuous. 



Surface marked by line, closely arranged lamellose striae, which are abruptly 

 undulated on all parts of the body of the shell. This species resembles P. 

 attenuatum, but differs in being arcuate from apex to base, in the gradual 

 attenuation towards the apex , and the closely incurved nucleus and less abrupt 

 expansion. 



Formation and Locality. Occurs iii the Comiferous limestone of the Devonian formation at the 

 Falls of the Oiuo, uii Uiu JieiUucky side of the river, 



Platyceras unguiforme. HALL. 



Platyceras unguiforme, Hall. Pal. N. Y., Vol. 3, p. 3221859. 



Shell oblique, arcuate, sub-spiral ; volutions one or two, more or less con- 

 tiguous at the apex ; last volution angular, extending in a straight or slightly 

 curved direction towards the aperture. Aperture oblique, sub-ovoid; peris- 

 tome sinuous' 



Surface longitudinally plicate, and marked by fine, crowded, undulating 

 lamellose striae. The plications are of unequal size; they are flat and broad 

 on the dorsal side, and angular and smaller on the ventral side. These plica- 

 tions increase in number by bifurcation. 



Formation and Locality. Found in the Niagara limestone in the quarries east of the city of Louis- 

 ville, Ky. It is a rather rare shell. 



Platyceras ventricosum. CONBAD. 



Plate XXV., figure 10. 



Platyceras ventricosum, Conrad. Ann. Rep. N. Y. 1840. 

 Platyceras ventricosum, Meek and Worthen. 111. Geol. Rep., Vol. 3 1868. 



Shell obliquely sub-ovate ; composed of two and a half to three very rapidly 

 enlarging contiguous, volutions, the last one of which is very large and ven- 



