46 



turns an obtuse angle and passes slightly forward to the median 

 line on the ventral side. This forms a bifid lobe and a short nar- 

 row saddle in the middle of the ventral side. There are, there- 

 fore, five saddles, and four lobes, but the middle saddle and two 

 middle lobes are produced by a bifid lobe. 



The septa in this species are very much like the septa in G. 

 lunatus, and the open umbilicus is very much like that in G. 

 greencasilensis, but the species do not agree in any other respects, 

 Rnd on the whole, have little resemblance to each other. The 

 reader must notice that in looking at figures 5 and 16 he is look- 

 ing, on the ventral side of the shell toward the apex, and in all 

 other ventral views he is looking toward the anterior end of the 

 shell, and, therefore, the septa in figures 5 and 16 are wrong side 

 up, and the saddles are on the lower side of the septa. Figures 

 4 and 17 are correct. 



Found by the late Wm. McAdams, in the Coal Measures, in 

 Montgomery county, Illinois, and now in the collection of Wm. 

 F. E. Gurley. 



GONIATITES JESSIES, n. Sp. 



Plate V, Fig. 18, lateral view of a small specimen; Fig. 19, end view 

 of a volution and part of a ventral view; Fig. 20, 

 surface view of a septum. 



Species medium or above medium size, discoid, sublenticular, 

 volutions rapidly expand, and periphery sharply rounded. We have 

 a specimen more than twice as large as the one that is illustrated, 

 but it shows none of the septa. Transverse section of a volution 

 crescentiform. The sides of the volutions are broadly rounded and 

 the ventral margin more narrowly rounded. The outer volution 

 embraces all the inner ones and closes the umbilicus. The dorso- 

 ventral diameter including the horns of the crescent is about one- 

 half more than the greatest transverse diameter, but the dorso- 

 ventral diameter increases rather more rapidly than the transverse. 

 The external shell is unknown. The air chambers are of medium 

 length. 



Each septum curves gently from the umbilicus forward and 

 back, to a point posterior to the place of beginning and near the 

 ventro- lateral margin, where it makes a narrow retral bend and 

 curves forward and backward forming half an ellipse, and then 

 makes a retral bend across the periphery of the ventral side. It 

 is not clear from our specimen whether or not there is a small 

 lobe at the median line. There are, therefore, four saddles and 

 three lobes in each septa as shown by the illustration. 



