164 PALEONTOLOGY OF KENTUCKY. 



marked by a strong fold, indicating a sinus in the margin of the peristome 

 commencing at an early stage of growth. Aperture somewhat oval, longest 

 in the dorsal-ventral axis. 



Surface marked by wrinkled, concentric striae, which are strongly undulated 

 at the base of the spines, and often abruptly bent backward at other places. 

 Spines scattered, comparatively strong and few in number, from five to fifteen 

 on the whole shell. The specimen before me, a most perfect one, with the 

 exception of a few broken spines, is a complete hollow shell from apex to 

 aperture, without defect ; it shows eleven spines. 



Formation and Locality. This shell was presented to me by Major Win. J. Davis, who found it 

 in the upper strata of the Devonian formation, in Clark county, Indiana. I have no doubt that this shell 

 is related to P. dumosum, but it differs sufficiently from it to constitute a distinct species,"and not merely 

 a variety. It is certainly as far removed from P. dumosum as P. multispinosum, and if that is considered 

 a good species, I think our shell has the same claim. It ought to be called simply Platyceras rarispinum. 

 It differs by the smaller number of spines, and by its different shape from P. dumosum, and besides, it is 

 never found with the latter in the same strata, but occupies a higher horizon. 



Platyceras echinatum. HALL. 



Plate XXXI., figure 21. 



Platyceras echinatum, Hall. Descript. of Xew Foss. 1861. 

 Platyceras echinatum, Hall. 15th Kep. N. Y. St. Cab. 1862. 

 Platyceras echinatum, Hall. Illust. of Dev. Fossils 1876. 

 Platyceras echinatum, Hall. Pal. N. Y., Vol. 5, pt. 2, p. 131885. 



Shell small ; apex closely incurved for about one and one-half volution ; the 

 body-whorl occupying about one volution, very ventricose ; rapidly expanding 

 from the first volution, giving the shell an obliquely conical form. Aperture 

 nearly circular or broad oval ; peristome sinuate ; the lines of growth and fine 

 striae conforming in direction to the outline of the margin. Remains of 

 revolving lines are sometimes traceable when the shell is not exfoliated. 

 Besides the concentric and obscure revolving striae, the surface is studded 

 with numerous nodes or fine spines, which are as much crowded as the figure 

 21, plate 31, shows, but they are not quite so regularly arranged as in the 

 illustration. The specimen before me has preserved the shell, but of the 

 spines only short stumps are visible ; the spines perished by the process of 

 silicification. In regard to size, this species varies from half an inch to an 

 inch and a quarter in length, and in large specimens the greatest diameter 

 of the aperture is one inch. This form could be the young of P. dumosum, 

 and would probably be considered as such if it occurred with that species in the 

 same strata or horizon, but this is not the case. It is never found associated 

 with P. dumosum, but occurs at a much higher horizon, and for that reason 

 must be considered as a distinct species. 



Formation and Locality. Found in the upper strata of the Devonian formation, in Clark county, 

 Indiana. It is not often met with. 



