XVII] THE COMPARISON OF RELATED FORMS 1067 



the diagram of this sktill we select a number of points obviously 

 corresponding to points where our rectangular coordinates intersect 

 particular bones or other recognisable features in our typical 

 crocodile, we shall easily discover that the Hues joining these points 

 in Notosuchus fall into such a coordinate network as that which 

 is represented in Fig. 527, c. To all intents and purposes, then, this 

 not very complex system, representing one harmonious "deforma- 

 tion," accounts for all the differences between the two figures, and is 

 sufficient to enable one at any time to reconstruct a detailed drawing, 

 bone for bone, of the skull of Notosuchus from the model furnished 

 by the common crocodile. 



Fig. 528. Pelvis of (A) Stegosaurus; (B) Camptosaurus. 



The many diverse forms of Dinosaurian reptiles, all of which 

 manifest a strong family likeness underlying much superficial 

 diversity, furnish us with plentiful material for comparison by the 

 method of transformations. As an instance, I have figured the 

 pelvic bones of Stegosaurus and of Camptosaurus (Fig. 528, a, b) to 

 shew that, when the former is taken as our Cartesian type, a slight 

 curvature and an approximately logarithmic extension of the x-axis, 

 brings us easily to the configuration of the other. In the original 

 specimen of Camptosaurus described by Marsh*, the anterior portion 

 of the iliac bone is missing; and in Marsh's restoration this part 

 of the bone is drawn as though it came somewhat abruptly to 

 a sharp point. In my figure I have completed this missing part 



* Dinosaurs of North America, pi. Lxxxi, etc., 1896. 



