42 



Each septum arises from the umbilicus and makes a broad curve 

 backward beyond the middle of the side, where it makes a sharp 

 retral angle and then curves forward and backward forming more 

 than half an ellipse, and, instead of arching over the middle of 

 the periphery, abruptly curves forward a short distance, and then 

 backward and forward so as to make this lobe bifid, and to form 

 a short narrow saddle in the middle of the ventral side. There 

 are, therefore, five saddles and four lobes, but the middle saddle 

 and two middle lobes are very small. The course of a septum is 

 best understood by looking at the illustration. It will be observed 

 that the courses of the septa, in this species, are the reverse of 

 those in the species above described. That is, to form the first 

 lobes, they are directed backward in this species, and forward in 

 those above described. The bifid saddle is directed forward, in 

 the species above described, and, in this, the curve crossing the 

 middle of the ventral side is directed backward, and we have a 

 small central saddle instead of a small central lobe, etc. The sur- 

 face of the shell is marked by fine, transverse, imbricating lines 

 of growth. 



This species is distinguished by its general form, transverse 

 lunate section of the volutions, fine transverse lines of surface or- 

 namentation, and peculiar sinuosities of the septa. 



Found by Geo. K. Greene in the Coal Measures, on Elkhorn 

 Creek, in Kentucky, and now in the collection of Wm, F. E. Gurley. 



GONIATITES ILLINOISENSIS, n. sp. 



Plate V, Fig. 6, lateral view; Fig. 7, ventral view; Fig. 8, sur- 

 face form of a septum. 



Species medium size, subglobose, volutions moderately enlarging* 

 and periphery broadly rounded. Oar specimen exposes part of 

 three volutions, leaving the impression that a complete shell con- 

 tains not less than six volutions. A transverse section of a volu- 

 tion is subcrescentiform, the horns being short and obtuse. The 

 last volution encloses all the inner ones, but leaves a rather large 

 open umbilicus. The air chambers are short and complicated. The 

 outer shell is not preserved in our specimen. 



Each septum may be seen to curve backward across the obtuse 

 end of the horn of the crescent, within the cavity of the umbili- 

 cus, and form an acute angle at the mouth of the umbilicus, where 

 it curves forward and then backward, in a waving line, to an acute 

 point, which is posterior to the first angle, where it makes a sharp 

 retral angle and curves forward, in a waving line, anterior to the 



