CONTRIBUTIONS TO PALAEONTOLOGY. G7 



This species differs conspicuously from either of the preceding in the 

 form of the volutions, and particularly in the arching node-like processes 

 on the dorso-lateral angles. 



Geological formation and locality. In the Upper Helderberg limestone: 

 Oneida and Schoharie counties, and in the Helderberg mountains. 



GYROCERAS NEREUS ( n. s.). 7 / ^ ^ ^^ 

 Shell subdiscoid, making a little more than one volution. Volutions 

 rotund, somewhat rapidly increasing in size : section nearly cir- 

 cular; septa, in the middle of the last volution, distant about 

 one-fifth of an inch. 

 Surface marked by fine undulating strise of growth, and, at une- 

 qual distances of a little less than a line, the shell is produced in 

 sharply undulating lamellae, which are produced at right angles 

 to the axis of the shell. 



In this external character, the shell differs from the other species in this 

 formation. In a specimen of medium size, there are eight of these lamelli- 

 form ridges in the space of an inch ; and in another larger individual there 

 are seven in the same distance, "while towards the apex there are twelve. 

 The greatest extent across the volutions is six inches. The Lest specimen is 

 flattened, so that the proportions cannot be fully determined. 



Geological formation and locality. In the Corniferous limestone : at 

 Auburn, N.Y. 



GYROCERAS ERYX(n.s.). 

 Shell large, making one or two volutions. Volutions very rotund, 



gradually expanded to the outer cavity, which appears to be 



proportionally a little wider and very deep. 



The specimens which I have seen are all imperfect, but could not have 

 made less than one and a half volutions. One specimen consists of a part 

 of the septate portion of a small or medium-sized individual, and, makino- 

 nearly two-thirds of a volution, measures about four and a half inches across 

 the disc : at the larger end, the dorso-ventral diameter is an inch and a 

 half; and at the smaller end, nearly an inch. At the smaller end of this 

 specimen there are eight chambers in the space of an inch ; and at the larger 

 end, nearly five in the same distance measured upon the side of the volution. 

 A larger specimen, which appears to be nearly complete at the aperture 

 and makes the greater part of one volution, measures eight inches from the 

 outer sides across the disc : this diameter may have been a little increased 

 1861.] 



