226 Reviews — Dr. Wheelton Hind's Chart of Fossil Shells. 



The lengthening of the mandible seems to have reached its maximum 

 degree in the Middle Miocene, after which it again became shortened 

 by the reduction of the symphysis, while the fleshy and now mobile 

 proboscis was left behind as the sole organ of prehension. 



In the upper dentition the chief changes are the loss of incisors 

 Nos. 1 and 3, and the great increase in size of incisor No. 2, which 

 eventually forms the great tusk characteristic of the later Probosoidea. 

 The canines are soon lost. In the earliest forms, some at least of 

 the cheek-teeth (milk-molars) are replaced by premolars in the 

 usual manner, and these teeth remain in wear simultaneously with 

 the true molars ; but in later forms no vertical succession takes 

 place, and as the milk-molars are worn they are shed, being replaced 

 from behind by the forward movement of the molars. Of these 

 also the anterior may be shed, until at length in old individuals 

 of the later types the last molar is alone functional. The gradual 

 increase in the complexity of the proboscidean molars is one of 

 their most striking characteristics. All stages can be traced between 

 the simple, brachyodont, bilophodont (quadritubercular) molars of 

 Moeritherium (Middle Eocene) to the extraordinarily complex type 

 of tooth found in Elephas. Thus in Palceomastodon (Upper Eocene) 

 the molars are trilophodont, and the same is true of the first and 

 second molars of Tetrabelodon (Miocene), in which, however, the 

 last molar is complicated by the addition of further transverse 

 crests. In the Stegodonts of the Siwalik Hills (Pliocene) a further 

 increase in the number and height of the crests takes place, and 

 the whole crown of the tooth is more or less covered with a thick 

 coat of cement. Still later, the transverse crests become highly 

 compressed laminse united by cement, and these are as many as 

 twenty-seven in number in the Pleistocene Elephas primigenius and 

 the recent E. indicus. 



The evolution of the lower molars corresponds with that of the 

 upper molars. Of the lower incisors the middle and outer pairs 

 (Nos. 1 and 3) are soon lost, but the second pair remains functional 

 for a long geological period. When the symphysis becomes 

 shortened, these incisors are sometimes retained as vestiges (e.g. in 

 Mastodon americanus), but in the genus Elephas they have com- 

 pletely disappeared. 



I^ s ^v i:e3 'w s. 



I. — Chabt of Fossil Shells found in connection with the 

 Seams of Coal and Ikonstone of North Staffordshire. 

 By Wheelton Hind, M.D., F.E.C.S., F.G-.S., and John Stobbs, 

 F.G.S. (Published by the North Staffordshire Institute of 

 Mining and Mechanical Engineers, 1903. Price 5s.) 



IT is an acknowledged fact that, compared with many other com- 

 mercially less important geological formations, very little is 

 known about the distribution of the fossils among the Coal- 

 measures. In this respect the North Staffordshire Coalfield has 

 been more carefully searched than others, though outside the 



