CEPHALOPODA. 453 



surface stria? are coarser. It differs from G. Patersoni in the volutions being 

 more exposed in the umbilicus ; in the broader and shallower median saddle, 

 and the lesser length and angularity of the lobes upon the lateral faces. 



Formations and localities. This species occurs in the Portage shales and sand- 

 stones, near Mount Morris, Livingston county; near Portland Harbor, Chau- 

 tauqua county ; above the lower falls at Portage, and in a similar geological 

 position at Truxton, in Cortland county. It also occurs in the Portage and 

 lower part of the Chemung group, near Ithaca, N. Y. 



GONIATITES PERACUTUS. 



PLATKS LXLX, FIG. 8 ; LXXIV, FIG. 11 



Gfoniatites perarutus. Hall. Illustrations of Devonian Fossils: Cephalopoda, pi. 69, fijj. 8. lS7fi. 



The only specimen observed is a fragment, which has been extremely 

 macerated, and the surface-characters entirely removed. The form has been 

 discoid; and it may be inferred that the transverse section was semi- 

 elliptical. 



The inner volutions are embraced in the outer one; the rate of their 

 enlargement cannot be estimated. The umbilical depression is narrow in 

 the cast, and the inner volutions were probably not at all exposed in the 

 shell. 



The fragment preserves a small portion of the chamber of habitation, and 

 a few of the air-chambers. 



The septa, from their origin, curve a little forward, continuing in that 

 direction nearly to the middle of the lateral face of the volution, when they 

 curve abruptly backward on a line almost parallel with the periphery, 

 describing a deep, obliquely semi-elliptical lobe, which, measured from the 

 summit of the saddle at the most advanced curve of the septa to the bottom 

 of the lobe, has a depth equal to the semi-diameter of the volution. From 

 the bottom of this lobe the septum advances abruptly forward, describing a 

 very acute saddle, the summit of which is within a few millimetres of the- 

 periphery, and thence abruptly recurves and passes over the margin of the 

 disc. k 



