60 NEW YORK STATE MUSEUM 



of opercula among the Swedish shells, which have not been observed 

 with typical species of Horiostoma — an argument to which little weight 

 can be given. Horiostoma, however, was described as having the final 

 whorl free about the aperture though only for a short distance, a feature 

 which is not specifically noted by Lindstrom for the Siluric species. 

 Koken has expressed 1 the belief that there is a palpable difference in the 

 typical Horiostoma (H. k o n i n c k i Oehlert) and the species referred by 

 Lindstrom to that genus, and regards the former as related to the capulids, 

 while the latter are derivable by easy stages from Euomphalus. Koken 

 has proposed to denominate the Swedish Horiostomas by the term Poly- 

 tropis de Koninck, introduced for Carbonic shells in 1881. As this name 

 however was employed by Sandberger in 1874 for an entirely different 

 group of Gastropods, its use is not permissible. 



Koken has not made out a very forcible argument for the distinction 

 of these genera ; and our impulse is to array the species from the Guelph 

 which we are about to discuss, under Munier-Chalmas's genus. Admitting 

 however the dependability of Koken's inferences, there remains no place 

 here for the term Polytropis which he has applied to the Swedish species 

 and which Whiteaves, following that proposition, has also employed for 

 species of the Guelph of Ontario. Hence we have introduced the name 

 Poleumita, basing its characters as a genus on the species which is most 

 abundant in the Guelph horizon at Rochester, P. scamnata. 



Poleumita scamnata sp. nov. 



Plate 9, fig. 1-8, 10, 12-15 



Shell turbinate, with spire more or less depressed, there being in this 

 respect a notable variation among the individuals ; whorls five to six, sub- 

 circular to subovate in section, very slightly overlapped by succeeding volu- 

 tions, on the contrary separated by a broad and deep suture, above which 

 the whorls stand up prominently. The form of the whorl does not vary 

 materially with growth, but the suture and its excavated or flattened outer 

 slope become more conspicuous though relatively no larger on the later 



1 Neues Jahrb. fur Mineral. Beilageband 6. 1889. p. 425, 477. 



