356 Dr. J. E. Gray on the Dentition of Rhinoceroses. 



XLI. — On the Dentition of Rhinoceroses (Rhinocerotes), and 

 on the Characters afforded hy their Skulls. By Dr. J. E. 

 Geay, F.R.S. &c. 



[Plate XI.] 



In the 'Proceedings of the Zoological Society ' for 1867, and 

 in the ' Catalogue of Carnivorous and Pachydermatous Mam- 

 malia in the British Museum/ p. 295, I gave an account of the 

 skulls of the Rhinoceroses in the British Museum, and described 

 their dentition in the young and in the adult animals. Since 

 that period the British Museum has received several additional 

 specimens, which have enabled me to observe further details 

 of the changes that take place in the skulls and teeth during 

 their growth ; and I have been induced to condense in this 

 paper the results of their examination. 



The Asiatic Rhinoceroses have the front of the nasal bone 

 convex, produced, and more or less acute in front. 



The intermaxillaries in the skull of the very young animal 

 are spongy and united together in front, with two rudimentary 

 teeth on the hinder part of eacli side. In tlie older animals 

 these teeth are more elongate, produced, and separate from each 

 other in front, and supported by a more or less long process 

 of the intermaxillary bone, which encases the upper and outer 

 side of their hinder part. The young animals have two teeth 

 on each side, the hinder being the smallest ; but in the older 

 animals both these teeth drop out, and the front one is re- 

 placed by a large tooth, which eventually has a large flattened 

 crown. 



In the Asiatic one-horned Rhinoceroses [Rhinoceros] there 

 is a small cylindrical cutting-tooth on the inner side of the 



they can be divided into five principal groups, in whicli all sponges, inclu- 

 ding the Hexactinellidai and Calcispongise, may be included, thus : — 



1st. Sponges with horny fibre and granular axis without foreign objects. 

 Aplyshiidce. 



2nd. Sponges with horny fibre, amorphous sarcode, and axis of foreign 

 objects. Herciniadce. 



8rd. Sponges with horny fibre and axis of proper spicules only, t. e. 

 spicules formed by the species. Chalinidce. 



4th. Sponges with horny fibre and axis of proper spicules, more or less 

 echinated also with proper spicules. Annates. 



5th. Sponges in which the fibre is formed of proper spicules cemented 

 together by amorphous sarcode. Renierince. 



It should always be remembered that the materials of the axis cannot 

 get into the fibre after the latter is formed, and therefore that the sponge 

 must aiTange all this beforehand. 



In a short time I hope to go further into this subject, as I have com- 

 pleted the 1st and 2nd divisions so far as subgrouping goes. 



