12 Watson, The larger Coal Measure AmpJiibia. 



the splenial is entirely a bone of the outer side of the jaw, 

 as is the first infradentary of the Crossopterygian nnandible. 



The details of the structure of the lower jaw of 

 Pteroplax cannot be made out, but it seems to me 

 essentially similar to that of Loxomnia, modified by the 

 development of two enormous internal vacuities. 



Large numbers of vertebrae and ribs occur in the 

 collection, all very similar and all typically embolomerous, 

 the intercentrum being a complete ring nearly as big as 

 the centrum. Typical embolomerous vertebrae are defi- 

 nitely associated with each type of skull. There seems 

 to be little doubt that this type of vertebra is primitive 

 in the large Stegocephalia, the ordinary rachitomous type 

 being almost unknown in the coal measures and becoming 

 commoner in later times. 



I wish to express my thanks to the Council of the 

 Northumberland and Durham Natural History Society 

 for the opportunity of describing this important material 

 and to Mr. E. L. Gill, the curator of the Newcastle 

 Museum, for his many kindnesses whilst working on it. 



