GASTEROPODA. 27 



" Locality. Near Schoharie, in Onondaga limestone." 



A specimen, which has been supposed to represent the original of Mr. Con- 

 kad, is illustrated in figs. 25 and 26, plate 9. The apparent band bordering 

 the suture is caused by a narrow depression of the surface, parallel with 

 the suture, from which the striae rise abruptly and bend forward, leaving a 

 narrow depressed line or canaliculation along the suture. It has not the 

 denned band of Pleurotomaria, and the recurving of the striae is less distinct 

 and abrupt than in some other specimens of Platyostoma. 



Formation and locality. In limestone of the Upper Helderberg group, Scho- 

 harie, N. Y. 



Platyostoma unisulcata var. 



PLATE XI, FIGS. 1-3. 

 Platyostoma unisulcata var., Hall. Illustrations of Devonian Fossils: Gasteropoda, pi. 11. 1876. 



This form, from the Hamilton group at West Bloomfield, N. Y., has so much 

 the form and aspect of Mr. Conrad's original figure ut cit., except in the lesser 

 elevation of the spire above the last volution, and the absence of a sutural 

 band, that I have placed it under the above designation. 



Platyostoma turbinata. 



PLATE IX, FIGS. 12-24. 



Platyostoma turluii/ita. Hall. Fourteenth Rep. N. Y. State Cab. Nat. Hist., p. 106. 1861. 

 <• «« " Illustrations of Devonian Fossils: Gasteropoda, pi. 10. 1876. 



Shell rabtarbinate, sometimes approachinga subglobose form. Spire depressed, 

 or more or less elevated above the outer volution, sometimes nearly on 

 the same plane; volutions three or four, rapidly expanding, the last 

 extremely ventricose, with the lower part projected in the direction of 

 the columella, which is much extended. Aperture subovate, broader 

 above, narrowing and often extended below. 



