GASTEROPODA. 39 



Pleurotomaria. This feature is not observed on the last volution, which is 

 marked on one specimen by a faint carination near the upper part ; on the 

 lower side of the volution are four or five revolving carinate bands. 



The features preserved are altogether like those of Cyclonema, and in the 

 absence of other evidence, it is thus referred. 



Formation and locality. In a calcareous band of the Chemung group at 

 Nichols, Tioga county, N. Y. 



LOXONEMA, Phillips. 



In the Schoharie grit, and in the limestones above this rock, there are 

 numerous casts of spiral univalves, which, though evidently belonging to 

 forms like Loxonema or Murchisonia, cannot readily be distinguished in the 

 absence of surface markings. Several species of these genera have been 

 described {Fourteenth Report on the N. Y. State Cabinet Nat. Hist.) from specimens 

 retaining the external characters. There are other forms still, which, although 

 we have no examples with the shells preserved, nevertheless differ so widely 

 in their form and proportions from those already described as to be distin- 

 guished by these characters alone. 



One of these from the Schoharie grit has nearly the form and propor- 

 tions of L. altenuata of the Upper Pentamerus limestone, and in the casts no 

 positive means exist of pointing out characters which will distinguish the one 

 from the other. Specimens resembling the L. compacta, of the same geological 

 formation, upon a careful comparison, show the volutions to be more rotund, 

 and the spire more rapidly ascending. The determination of species in this 

 condition is attended with many difficulties, and in the end there must still 

 remain some doubt, when the differences of form and proportions may have 

 been disguised by pressure or . accident. Under these circumstances, I have 

 characterized several species among the specimens which are only known in 

 the condition of casts ; leaving a more satisfactory determination to the future, 

 and a collection of better specimens. 



