PLATE 7 . 



Page. 



Figs. 1 and 3. Prionocyclus Woolgari 455 



1, a. A side view of an imperfect specimen, somewhat less than half grown, showing the large 



cremilations of the keel, etc. 

 1, b. A peripheral view of the same ; one side being defective. 

 1, c. A side view of a smaller specimen, with the .cremilations of the keel and the nodes of 



the eosta? less strongly defined. 

 1, il. A peripheral view of the same. 

 1, e. A septum, magnified about two and a 'half diameters, from a specimen intermediate in 



size between the last two. 

 1,f. A still smaller specimen, with the cremilations of the keel and the nodes of the costal 



only just beginning to bo developed. 

 1, g. A large specimen, showing the modifications of the keel, eosta', and nodes in the adult 



shell.' 



1, h. A part of a septnm, consisting of the siphonal lobe and the first and second lateral lobes 



and sinuses, magnified about one and a half diameters from the large specimen rep- 

 resented by fig. 1, g. 

 3. A fragment of non-septate part of an adult specimen, apparently of this species, showing 

 the keel merely represented by low, isolated, elongated nodes, and the nodes at the 

 outer ends of the eosta' developed into large spine-like projections. 



Fig. •-'. Mortoniceras Vermilionhnsk 450 



2, a. A side view of apparently a young individual (type-specimen). 



2, b. A septum of the same, magnified to a little more than four diameters. 



