348 D. 31. S. Watson — Rejjtilian Femur from Scotland. 



of the bone is not unlike that of Ctenodus, and was no doubt the 

 reason of its place in the collection. 



The very small piece of matrix which is preserved is identical with, 

 that of some of the fish from the No. 2 Ironstone, Loanhead, and diif ers 

 from any other fish-bearing matrix that I know in Britain. [Any 

 one with experience of Carboniferous fishes will recognize that it is 

 usually fairly easy to identify the important localities (the Loanhead 

 ironstones, the various Staffordshire ironstones, etc.) by inspection of 

 the matrix.] Despite the fact that it was not localized, I think that 

 the probability of its being from the Loanhead ironstones is sufficient 

 to justify a description. 



Mr. Herring's excellent photographs reproduced in Plate XXVII 



will give a much better idea of the bone than any description. The 



head shows a large half-moon shaped area for an articular cax'tilage, 



-and is directly continuous with the small trochanter, which is carried 



on by a sharply marked ridge down the rather stouter shaft. 



There are two rather unusually distinct condyles at the lower end 

 which were also covered by a cartilaginous cap during life. That 

 this little femur is of reptilian type is obvious ; it resembles closely 

 that of Trispondylus and even those of certain Pelycosaurs. Such 

 Cotylosaurs as Labidosaurus only differ in their more pronounced 

 trochanter. The only amphibian femora which at all resemble it are 

 those of Trematops and the Lower Carboniferous Pholidogaster. Both, 

 however, differ in their much less distinctly divided lower end, but do 

 resemble it sufficiently to suggest that it is not inconceivable that 

 it is really a precociously advanced Stegocephalian. 



I showed some time ago that the Carboniferous Embolomerous 

 Stegocephalia (which are known from the Burdiehouse Limestone) 

 resemble the Cotylosaurs, particularly Seymouria, much more closely 

 than do any later amphibia, and suggested that the reptiles arose 

 from the Stegocephalian stock at its base. If the bone figured in this 

 paper be really a reptile, and if it really comes from the Loanhead 

 ironstone, it affords strong additional support to this view, for it is 

 nearly as old as the oldest known Stegocephalian bones and much 

 more ancient than any previously known reptile. In any case it is 

 most probable from general experience that the reptiles did arise 

 from the base of the amphibian stem, or all its later members by 

 adopting some specialization have lessened their potentiality, just as 

 the cells of an embryo when once divided into epiblastic ancl endo- 

 blastic layers are no longer individually capable of giving rise to the 

 whole animal. 



There is no doubt that this femur represents a new type, and 

 I am glad to have an opportunity of expressing the pleasure that 

 Dr. Traquair's papers have always given me by calling it Fapposaiinis 

 Traquairi, gen. et sp. nov. 



EXPLANATION OF PLATE XXVII. 



Type femur of Papposaurus Traquairi, gen. et sp. nov. x 1. A, dorsal aspect ; 

 B, ventral aspects; C, fibial side; D, tibial side; E, proximal end; 

 F, distal end. ? Lower Carboniferous of Scotland. 



