PTEROPODA. 175 



Otsego county, both in the shale and in limestone nodules, and is abundant in 

 the upper part of the shale near Alden, in Erie county. It also occurs in the 

 soft shales of the Hamilton group on Canandaigua lake. 



S T Y L I L A , Lesueur (1826). 



CRESEIS, Rang (1829). 

 Styliola, Lt'siuur, Ludwig, Richter, Hall. 



In 1864, Prof. Rudolph Ludwig (Palaontographica XI) proposed to restrict the 

 generic term Tentaculites to the annulated forms, in accordance with the 

 original definition of the genus ; and placed under the genus Styliola, of Le- 

 BUSUB, all the smooth forms, or those which are either longitudinally or 

 transversely striated, but without annulations. 



In 1865, 1866 and 1867, Dr. R. Richter (Zeitschrift der Deutsch. Geol. Gesell- 

 schaft) adopted the same distinction among these fossil forms heretofore referred 

 to the genus Tentaculites. 



t In 1867, M. J. Barrande has maintained the same view, and described 

 Sti/liolu clavuha, from the Bohemian strata of Devonian age, in his Systeme 

 Silurien du Centre de la Bohtme. 



"9f W W ^f -rf "9r ^F ^r ■tF * * •?(* 



The following definition of the genus, as given by Prof. Ludwig, is translated 

 from the work of ML Barrande : 



Generic characters: " Shell small; transverse section circular ; closed below, 

 , and thicker than in the upper part ; conical. Surface without annulations, 

 smooth, but with fine strire of growth, and sometimes with fine longitudinal 

 stii;i-, without longitudinal slit, but sometimes with one or two longitudinal 

 grooves, which do not pmetrate the shell; without operculum, and without 

 . interior partitions, but having a persistent point, sometimes curved backward. 

 The greatest width is at the opening, which is oblique or normal to the axis of 

 the shell." 



This definition of the genus, applied to the American forms known to us, 

 renders the distinction between Tentaculites and Styliola sufficiently clear. 

 M. Bauuande has remarked, with much reason, that from the nature of these 



