150 



Annals of the Carnegie Museum. 



in the shallower cameras. As may be seen by the figured specimen 

 the older cameras are nearly as deep as those in Geisotwceras normale, 

 but on approaching the living chamber they become very shallow. 

 The siphuncle is very small, and is situated close to the center. Liv- 

 ing chamber and siphonal funnels not seen. A few specimens show 

 traces of faint longitudinal striae. 



A specimen of this shell was sent to Dr. Holzapfel, who compared 

 it, on account of its very shallow cameras, with Orthoceras gregarhim 

 Munster ((9. angiistiseptatum Giimbel). 



Locality. — This species occurs rather rarely in the red shales of the 

 Upper Devonian at Three Forks, Montana. 



Order AMMONOIDEA. 



Suborder GASTROCAMPYLI Hyatt. 



Family CLYMENID^ Gumbel. 



Genus Platyclymenia Hyatt. 



Platyclymenia americana Raymond. 



(Plate VI, figures 10-13 ; Plate VII, figures 1-3.) 



Clynienia [Plalyclytnenia) americana Raymond, I907. '^American Journal of 

 Science,'^ series 4, Vol. XXIII, p. 118, figures. 



This is by far the most abundant of the cephalopods in the red fis- 

 sile shale and is also quite common in the green shale. Although a 

 great number of specimens have been collected, most of them are so 

 poorly preserved that they are useless for study. 



Description. — Shell of medium 

 size for the genus, compactly coiled, 

 but not involute. The whorls are 

 depressed in section, the venter of 

 the inner whorls flattened, that of 

 the living chamber more convex. 

 The living chamber is large, con- 

 sisting of over half a volution. 

 The cameras are rather shallow on 

 the inner whorls, become deep in 

 the adult, and then suddenly be- 

 come so shallow that the septa are 

 twice as numerous as before. The 

 sides of the whorls are crossed by strong ridges which have a slightly 

 diagonal trend and which die out on the umbilical margin and on the 



Y\G. I. Platyclymenia americana 

 Raymond. Outline drawing of the type 

 and of a fragment to show sutures. 

 Natural size. 



