CEPHALOPODA— PROTOCHOANITES. 



39 



Subclass TETRABRANCHIATA. 



Order L NAUTILOIDEA. 



Suborder Protochoanites* Grabau and Shimer. 



I. VoLBORTHELLA Schmidt. 



Minute, primitive orthoceracones with expanded, living chamber, 

 conical septa and small, empty siphuncle. Cambric. 



I. V. tenuis Schmidt. (Figs. 1232, 1233.) Cambric. 



Small, rather rapidly tapering; septa deeply arcuate. 



I I 



Fig. 1232, Volborthella tenuis. A 

 slab with several individuals, X'- (After 

 Schmidt. ) 



Fig. 1233. Volborthella tenuis. En- 

 largement of the specimens. (After 

 Matthew.) 



Protolenus beds (base of Middle Cambric) of New Bruns- 

 wick and Europe. 



Suborder Holochoanites Hyatt. 



II. Cameroceras Conrad (emended Hyatt). 



Orthocones, with large, excentric siphuncles, having the siphonal 

 funnels extend to the preceding septum, and supplemented by an 

 " endosipholining " or inner lining tube, and with funnel- form 

 endosiphuncular filling (endosiphosheaths) only in connection 

 with the living chamber, and with an endosiphotube in the center 

 which may continue in the form of a compressed slit-tube (endo- 

 siphocoleon ) . Ordovicic-Siluric- 



2. C. (Proterocameroceras) brainardi (Whitfield). (Fig. 1234.) 



Ordovicic. 



Large (up to 4 ft. or more in length), expanding very gradually 



( I in 30 mm.) ; cross section elliptical; camerse with depth about 



one fifth of the width; septa from 3-4 mm. distant. Endosipho- 



