114 



Repokt of the State Geologist. 



angulation appears to be confined to the first half of the protoconch. This 

 characteristic shape is well displayed in the accompanying figures. 



Form of the earlier whorls. The whorl at the commencement of the first 

 volution is very narrow and crescentiform in section, but its relative width is 

 nearly doubled before this volution is completed This continued rapid 

 increase in dorso-ventral width renders the first three or four volutions highly 

 convex, the second and third being very rotund. Gradually there follows a 

 lateral compression of the whorl lessening its rotundity and eventuating in the 

 elongated lunuliform section of the mature shell. 



Umbilication is minute but distinct until the close of the third volution. 

 Its maximum, however, appeal's to be not at the commencement of the overlap 



91 92 93 



Figures 91, 92. Tornoceras uniangulare. Lateral and ventral views of a shell ol two volutions, showing the 

 open umbilicus, the course of the septa and the incipient ventral ridge, x 23. Fig. 93 A young shell smaller 

 than that represented in figures 91, 92, but wilh less umbilication. x 25. 



of the protoconch by the first whorl, but at the end of the primary volution. 

 Thenceforward there is a regular decrease of umbilication until it disappears 

 at the very early age specified by the projection of the recurved edge of the 

 stoma which eventually forms an erect projecting callous filling the umbilicus. 



Sutures. At maturity the suture has broad and very shallow magno- 

 sellarian saddles, a lateral lobe with an abrupt slope on the umbilical side, but 

 gently depressed on the venter to form a saddle of about the same size 

 although less strong than the lateral lobe ; the ventral lobe is narrow and acute. 

 In mature forms where the septa are close together (a normal feature) the 

 umbilical slopes of the ventro-lateral lobes of adjacent septa are almost con- 

 tiguous and their upward slopes often present the appearance of a continuous 

 revolving line. This effect is lost in earlier grow th stages where the septa are 

 more distant. The dorsal course of the suture is even more simple than its 

 ventral course ; it makes a single low saddle similar to the magnosellarian 

 saddles but longer and deeper, and a rather deep dorsal lobe. 



