GASTEROPODA. 23 



Platyostoma lineata var. callosa. 



PLATE X, FIGS. 22, 23. 

 Platyostoma lineata var. callosa, Hall. Illustrations of Devonian Fossils : Gasteropoda, pi. 9. 1876. 



This variety has the general form of specimens of P. lineata, except that the 

 spire is extremely depressed, being almost flat upon the top. The mouth is 

 suborbicular, with the peristome slightly sinuate on the upper side near its 

 junction with the preceding volution. The inner lip is marked by a thickened 

 callus, not observed in any other specimens, the callosity extending into the 

 lip below (as shown in fig. 22), which thence assumes the ordinary features of 

 the species. 



This variety is from the Hamilton group, near Geneseo, N. Y. 



Platyostoma lineata var. ampla. 



PLATE X, FIGS. 25, 26. 

 Platyostoma lineata var. ampla, Hall. Illustrations of Devonian Fossils : Gasteropoda, pi. 9. 1876. 



The specimen has had about four and a half volutions, the last one enlarging 

 very rapidly, and terminating in a broadly expanded aperture, as shown in 

 fig. 26. The margin of the peristome is slightly sinuate on the upper side, 

 and the columellar lip slightly grooved. The surface is marked as in other 

 forms of this species. 



This form corresponds very nearly with the outline figure of the species 

 P. lineata, given by Mr. Conrad, loc. cit. It is of rare occurrence, so far as my 

 own observations have gone, there being not more than five or six specimens 

 among a collection of several hundred of the ordinary forms from different loca- 

 lities. There are, however, so many intermediate phases as to leave no doubt 

 of the relations of the most extreme varieties represented in this and the pre- 

 ceding as well as the following form, which, if separated from their associates, 

 might be considered distinct species. Those indicated as P. defigurata and 

 P. euomphaloides may, perhaps, prove to be only varieties of the same species 

 when a larger collection of specimens shall be examined — those at hand, at the 

 present time, not furnishing the requisite data for uniting them with P. lineata. 



The specimen figured was found in the Hamilton shales, at Bellona, N. Y. 



