248 SMITH. [Vol. XVI. 



The adolescent S. chicoensis resembles in appearance and in 

 relative measurements the adults of 5. oregonensis, and very 

 probably is a descendant of the latter species. 



Ocairreiice and locality. — The material on which this paper 

 is based was collected by Mr. Frank M. Anderson, at the Forty- 

 Nine mine, one and one-half miles southwest of Phoenix, Oregon, 

 in beds supposed to belong to the Upper Horsetown formation, 

 top of the Lower Cretaceous, and described by him in " Some 

 Cretaceous Beds of the Rogue River Valley, Oregon." ^ The 

 writer's thanks are especially due Mr. Anderson for the gener- 

 osity with which he furnished the specimens to illustrate this 

 work. In a forthcoming paper, in the Proceedings of the Cali- 

 fornia Academy of Science, Series 3, Mr. Anderson will figure 

 and describe Schloenbachia oregonensis and the rest of this 

 interesting fauna. 



Ontogenic Stages. 



Nepionic or Larval. 



Phylembryonic. — The early embryonic stages are shell-less, 

 and necessarily cannot be represented in fossils, so the paleon- 

 tologist begins his investigations with the phylembryonic, when 

 the shell gland becomes functional, and the class or phylum 

 can be made out. This is represented in the ammonites by 

 the protoconch, which in this species is a smooth, oval, bobbin- 

 shaped body, a little wider than high, to which the chambered 

 coil is attached. With this stage begins the siphon, as a pear- 

 shaped sac, or caecum, taking up a large part of the entrance 

 from the protoconch to the chambered shell. The dimensions 

 of the protoconch are remarkably constant in a large number of 

 specimens ; those of the protoconch figured on PI. A, Figs. 

 1-3, are as follows : 



MM. MM. 



Diameter . . . 0.42 Width . . 0.48 



This stage is analogous to the protegiilum of the brachiopods, 

 protaspis of the trilobites, and prodissoconch of the pelecypods, 

 and corresponds to the primitive cephalopod. The embryonic 



"^ Journ. 0/ GeoL, vol. iii, No. 4. 



