1905.] 



PRIMITIVE REPTILE PROCOLOPHON. 



229 



in the imperfect example which adjoins the pelvis. Its proximal 

 end is about intermediate in form between the femur in a Chelonian 

 and in Oridthorhynchus ; for the under surface of the ai'ticular 

 head is a wide concave pit (text-fig. 37, 6), not without suggestion of 

 the bone in Saurodesmus and the small mammal from Stonesfield 

 and certain biixls. The trochanters on each side of the articular 

 head are much less developed than in the Monotreme, and the sub- 

 articular pit is less conspicuous in the other sjDecimens from Fern- 

 rocks than in the Donnybi-ook example, which may indicate other 

 species. The bone can best be compared with Pareiasauria. The 

 external or posterior trochantei- is produced down the shaft as 

 a slight ridge on the under side of the bone in one specimen. 

 The triangular section of the shaft is not so marked as in the 

 Donnybrook specimen, and the proximal end is more flattened on 

 the superior or anterior surface (text-fig. 37, «). The curvature of 

 the bone is distinctly sigmoid in length (text-fig. 37, c). Distally 

 it both thickens and widens to the articulation, where it is flat- 

 tened on the inner side, concave behind, with a pulley articu- 

 lation in front. One femur is longer and another shortei' than 

 the common type. There is no living reptile to which the bone 

 approximates. 



Tibia and Fihida. — The tibia is much stouter than the fibula. 

 Its proximal end is triangular, being flattened behind, more like 

 the tibia of a mammal than of a Dinosaur. Its wide proximal 

 end forms the larger part of the ai'ticulation with the femui'. 

 The bone is about f of the length of the femur (text-fig. 37, h). 



Text-fie-. 38. 



Humerus and adjacent bones of fore limb, from Fernrocks. 



The Fore Limb. — The fore limb was relatively small in the 

 Procolojyhon laticeps (Phil. Trans. 1889, pi. 9). The humerus is 

 considerably expanded at the proximal end, with a large radial 

 crest, and manifestly twisted in the shaft, much as in Aristo- 

 desmus and in many of the Anomodontia. But the distal end is 



