648 W. D. SMITH 



and 10, Fig. 3. The chief differences are the more gibbous form of 

 plenus, and minor variations in the serrations and digitations of the 

 suture. Up to the end of the larval stage, however, the two varieties 

 are quite similar in every respect, but, as far as the writer has observed, 

 plenus develops no nodes on the umbilicus. Number 8, Fig. 3, shows 

 plenus at a diameter of 3l mm where the great change in size of coil 

 comes in. No specimens of the variety plenus were found showing 

 a tendency to uncoil, and, furthermore, no crowding of the septa. 

 It appears to be more normal and less degenerate than any of the 

 forms studied. The young Scaphites nodosus Owen is very like, 

 practically indistinguishable from, that of brevis and plenus. This 

 variety has grown to its extraordinary size due, no doubt, to more 

 favorable conditions. The variety known as quadrangularis, whose 

 adult stage has been briefly described at the outset of this paper, 

 differs in the larval stage not materially from the other varieties. 

 In the adolescent and early ephebic stages there is, on the other hand, 

 quite a difference in the ribs, every fifth or sixth one being much 

 more pronounced. 



Phylogeny. — In studying the shape of the whorl, number of lobes 

 and saddle of the sutures, and the digitations in each, the umbilicus and 

 sculptures, the writer has been led to the conclusion that the Scaphites 

 nodosus group is to be considered as having come from some member 

 of the Stephanoceratidce, or "crown-shaped" ammonites. The writer 

 has compared the young stages of the Scaphites nodosus with 

 the young of Desmoceras hoffmani and D. beudanti, also with Son- 

 neratia stantoni, both from the Lower Chico of California and found 

 many general relationships. These similarities are found in (1) the 

 shape of whorl; (2) deep, narrow umbilicus; (3) number and digi- 

 tation of lobes and saddles in the sutures. 



However, there is one marked difference, but one which may be 

 easily accounted for in a way to be explained later, in the lobes of 

 the sutures of Scaphites and the forms just mentioned. Sonneratia 

 and Desmoceras have throughout their development triaenidian lobes. 

 The development of such lobes can be seen in Fig. 3, Numbers 2 

 and 3. This type of suture is the normal type according to Haug. 1 



1 Emile Haug, "Les Ammonites du Permian et du Trias," extract from the 

 Bulletin de la Societe Geologique de France, 3d series, Vol. XXII (1894), p. 385. 



