﻿lxxiv PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [>ol. lxxii, 



Lyme Regis, which he named Ischyodtos orthorhinus (now known 

 to be Prognathodus). The prolongation of the snout in this 

 early Jurassic fish is of precisely the same remarkable shape as 

 that in the existing Chimseroid Callorhynchus. Notwithstanding 

 the many changes which have occurred in Chimseroid fishes since 

 that remote period, including a total replacement of the genera, 

 the pattern of snout in one group at least has persisted. Again, 

 the existing Lamnid sharks are characterized by a curious dwarfing 

 of the third or fourth tooth, or both, on each side of the upper 

 jaw. A study of associated sets of teeth of some of the earliest- 

 known members of the family from the Chalk, proves that this 

 feature was already established even in Cretaceous times: not only 

 in the genera which have survived, but also in the extinct Gorax. 

 Finally, in the Society's Quarterly Journal for 1910, I pointed out 

 that in the Lower Jurassic carnivorous dinosaurian, Megalosaiirus, 

 three or four pairs of the teeth in front of the lower jaw are 

 diminutive, perhaps functionless. Last year, through Mr. W. E. 

 Cutler, the British Museum received from the Upper Cretaceous 

 of Alberta (Canada) the jaws of a gigantic Megalosaurian, 

 evidently of another genus, in which exactly the same reduction of 

 the teeth at the mandibular symphysis occurs. Through a wide 

 range of time and space, therefore, this small and apparently 

 insignificant feature persisted, and even passed from one genus to 

 another. 



The strength of heredity is, in fact, one of the most remarkable 

 phenomena with which a palaeontologist is repeatedly impressed. 

 Even when one great group gives rise to another, the later type 

 often seems to be handicapped at first by the inheritance of some 

 characters which are no longer congruous. The large majority of 

 the Permian and Triassic Reptiles, for example, although true 

 land-animals, still retained the large head and short neck which 

 were well adapted to the aquatic habits of their amphibian and 

 piscine ancestors. This was first strikingly shown by Seeley's 

 restoration of the South African Keirognathus, afterwards by 

 Boulenger's sketch of the Scottish T elerpeton, and has been 

 emphasized more recently by the numerous restorations of 

 Permian reptiles from North America by Williston, Case, and 

 others. Similarly, when Reptiles passed into Mammals, the 

 relatively-large tail of the gliding or swimming animal was no 

 longer needed ; but it persisted in nearly all Mammals at least 

 through the first half of the Eocene Period, and even at the 



