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PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [June 11, 



behind a plane at right angles with the distal articulation"*. This 

 description is drawn from the Cretaceous genus of Ichthyosaurians 

 found at Cambridge, and would apply but indifferently to most of 

 the genera from the Lias. This remark holds true in a less degree 

 for the following notes on the similitudes of the Ichthyosaurian 

 femur * : — 



" The femur, in shortness and strength, recalls some seals ; but in 

 arrangement of parts, the resemblance among mammals is closest to 

 Ornithorhynchus, which similarly has lateral trochanters extending 

 the width of the proximal end, though in Ichthyosaurus the tro- 

 chanters are not divided from the rounded articular head." " Among 

 crocodiles the only resemblances are that the articular ends of the 

 bone are compressed, the proximal one rounded and at right angles 

 to the distal end." " The two trochanters at the head of the femur 

 of Ohelydra, though not so well developed and not opposite to each 

 other, are homologous with those of the head of the femur in Ichthy- 

 osaurus ; but there is no other character in common in the limbs." 



Fig. 1. — Right Femur of Cetarthrosaurus Walkeri. 



a. Underside, b. View from the distal end. P. Proximal articulation. 

 T. Anterior trochanter. T'. Posterior trochanter. 



"With the type thus indicated, Cetarthrosaurus is closely comparable. 

 The specimen may be thus described : — 



The bone is 2-| inches long, subovate at the proximal end, and a 



* MS. Osteology of the Eeptilia. 



