54 PALAEONTOLOGY OF NEW YORK. 



side. The absence of a band or sinus on the periphery is, however, a dis- 

 tinctive feature. 



Formation and locality. In limestone below the " Hydraulic beds" at the Falls 

 of the Ohio. Communicated by Dr. James Knapp, of Louisville, Ky., and 

 Major S. S. Lyon, of Jeffersonville, la. 



EUOMPHALUS, Sowerby. 



Straparollus, Montfort; Phanerotinus, Sowerby. 



The material for the study of this group of fossils, in my possession, is 

 so meagre and unsatisfactory that I am not prepared to express any decided 

 opinion regarding the separation of the genera Euomphalus and Straparollus. 



The typical forms of the first, with angulated volutions and depressed spires 

 begin their existence in the Calciferous sandstone and continue, with wide 

 interruptions, to the Chemung period. The genus Ophileta of the primordial 

 rocks is, in some of its forms, not very different from the Devonian species 

 with rounded volutions, which are referred to Straparollus or to Euomphalus 

 indifferently. In habit of life and mode of growth the two forms were similar ; 

 both become septate and decollate in their earlier volutions. In one of the 

 angulated forms under consideration, the early volutions were rounded and 

 decollated by septation — the angularity being gradually acquired and increasing 

 to the aperture. 



I have preferred to adopt the name Euomphalus for this group of fossils, 

 using the name Straparollus in a subgeneric sense for those with close rounded 

 volutions, where the spire rises moderately above the plane of the outer volu- 

 tion. 



These again, by almost insensible gradations, pass into those forms where 

 tin- volutions are disjoined, constituting the genus Phankrotixus of Sowerby. 

 The figures on plate 16 offer examples of these phases, where it becomes 

 extremely difficult to draw a line of specific distinction between those with the 

 volutions in contact and those where they are perceptibly disjoined. 



