Bibliographical Notices. 31/ 



the Sarondis, a small stream entering the Rio Negro, about 120 

 miles N.W. of Monte Video, while an under jaw was procured at 

 Bahia Blanca. In this description there are some very able remarks 

 on the various affinities presented between the remains and the qua- 

 drupeds belonging to the Pachydermata, the Rodentia, Edentata and 

 Herbivorous Cetacea, to the first of which it is however more parti- 

 cularly referable. The name of Toxodon platensis has been applied 

 to this singular animal, the first or generic term relating to the 

 curved form of its teeth, the latter indicating the locality of its dis- 

 covery. The skull, which is figured of the natural size, on a large 

 folio folding plate, is in length two feet four inches, in breadth one 

 foot four inches. The subordinate dimensions and a description of 

 every part is minutely given, and the following deductions are made. 

 The teeth consist of molars and incisors, separated by a long dia- 

 stema or toothless space; in the upper jaw the former are fourteen in 

 number, seven on each side ; the incisors four, one very large and one 

 small in each maxillary bone ; but although the dentary system is de- 

 cidedly rodent, yet the number of the molar teeth, and their diminu- 

 tion of size as they advance towards the anterior part of the jaw, in - 

 dicate an approach to the Pachydermata ; at the same time it is ob- 

 served, the Capybara, in the increased size of the posterior grinders 

 and other particularities, presents a somewhat similar alliance to the 

 same tribe. The depth of the zygoma bespeaks the size of the mas- 

 ticatory muscles ; and the temporal muscles being also large, it is 

 presumed that the great incisors at the extremity of the jaws were 

 used like the canines of the hippopotamus to divide or tear up the 

 roots of aquatic plants. The osseous parts pertaining to the senses 

 of sight and hearing resemble those of the aquatic Rodentia and Pa- 

 chydermata. The aspect of the nostrils is placed upwards, as in the 

 herbivorous Cetacea; but in the bony structure they materially differ, 

 by having narrow canals of intercommunication between the nasal 

 passages and the frontal sinus. The articulating condyles of the 

 cranium indicate, that when the body of the Toxodon was submerged, 

 the head could be raised so as to form an angle with the neck, and 

 bring the snout to the surface of the water, without the necessity of 

 any corresponding inflexion of the spine. There is no evidence to 

 determine the character of the extremities, whether they were un- 

 gulate or unguiculate, while the structure of the nostrils will sug- 

 gest that the habits of the animal were not so strictly aquatic, as to 

 warrant the supposition that the under extremities were altogether 

 wanting. Altogether the discovery of these remains is one of the 

 most important which has been made for a long period ; and in the 



