45 



far anterior as the point of commencement at the umbilicus) and 

 terminates in an acute point at the middle of ihe ventral side of 

 the volution. There are, therefore, two complete saddles and a 

 half saddle on each margin of each volution and three intervening 

 lobes. The pecular shape of the septa will be most appreciated 

 by looking at the illustrations. 



This species is distinquished by its general form, open concen- 

 trically lined umbilicus, flattened volutions, surface ornamentation, 

 and by the form of the septa. 



Found in the St. Louis Group at Greencastle, Indiana, and now 

 in the collection of Wm. F. E. Gurley. 



GONIATITES SUBCAVUS, n. sp. 



Plate V, Fig. 15, lateral view; Fig. 16, end of a volution and 

 ventral view; Fig. 17, surface form of a septum. 



Species rather below medium size, subglobose, volutions slowly 

 expanding and broadly rounded from umbilicus to umbilicus. 

 Transverse section of a volution concavo-convex, and the trans- 

 verse section, where our shell is broken off, is three times as 

 much as the dorso ventral. The transverse diameter proportion- 

 ally diminishes toward the apex and increases toward the body 

 chamber. The number of volutions not known. The last volution 

 embraces all the inner ones and leaves a large open umbilicus 

 that is like a hollow cone and formed by the leveling of each 

 outer volution, from the inner volution, to the margin of the um- 

 bilicus. The shell on the interior of the umbilicus is smooth. 

 The shell is broadly rounded from one umbilicus to the margin 

 of the other leaving no lateral sides and the greatest transverse 

 diameter at the margins of the umbilici. The outer surface of 

 the shell is smooth. The air chambers are very short. Four fur- 

 rows arise outside of the margin of the umbilicus and curve for- 

 ward across the ventral side. These furrows do not interfere with 

 the margin of the umbilicus, they are smooth and exist on the 

 outer surface of the shell and on the cast. They do not regu- 

 larly occur on a volution and belong rather to the outer shell it- 

 self than to the body of the volution. It does not appear that 

 they could have had any effect upon the animal. 



Each septum arises from the umbilicus and makes a broad 

 curve backward where it turns an btuse angle and then curves 

 forward nearly as far anterior as the point of commencement and 

 then backward forming more than half an ellipse and again 



