ContiHbutions to Invertebrate Palaeontology. 613 



GoMPHOCEKAS SciOTENSE Wliitf. Page 531. 



Fig. 4. Side view of the outer chamber of the specimens Fig. 13 and 14, on 

 Plate VI, sliowing tlie depth of tlie septum. 



Gyeoceras SEMiNODOSUJt Whitf. Page 533. 



Fig. 5. Side view of the specimen described, sliowing the absence of nodes on 

 the inner whorls. On the dorsum of the outer volution a fragment 

 of the shell remains indicating its thickness. 



PLATE IX. 



GoMPHOCERAS Hyatti Whitf. Page 529. 



Fig. 1. Ventral view of the specimen figured on Plate VIII showing the 

 breadth of the specimen. 



Gomphoceras Sciotexse Whitf. Page 531. 

 Fig. 2. Diagram showing the form of the aperture and its relation to the 

 body of the shell as seen in a top view of the specimen figured on 

 Plate X. 



PLATE X. 



Mytilaeca percakinata Whitf. Page 523. 



Fig. 1. Vertical view of a left valve, the extremity of the hinge is restored in 



outline. 

 Fig. 2. View of the anterior side of the shell showing the depth of the shell. 



Trematoceras Ohioense Whitf. Page 528. 



Fig. 3. Lateral view of the specimen used for description showing the line of 

 nodes formed by the closing of the perforations, the upper one 

 being in the outer chamber was not entirely closed. 



Fig. 4. Section of the lower end of the specimen showing the form of the 

 siphon. 



Gomphoceras Sciotense Whitf. Page 531. 

 Figs. 6 and 7. Front and lateral views of the specimen showing the form and 

 the septa. For other figures see Plates VIII and IX. 



Gyeoceras Columbiense Whitf. Page 532, 

 Fig. 8. Lateral view of an imperfect internal cast of a specimen of about the 

 usual size showing indications of the arrangement of the septa. 



