9 o 



TORTOISES AND TURTLES. 



shields on the shell, the whole of these tortoises are characterised by the presence of 



an intergular (i.gu) shield between the two gulars (gu) on the front of the plastron ; 



such intergular shield being, as we have seen, but very rarely present in the 



S-necked group. Very generally among the present assemblage one or more of the 



pairs of costal bones of the carapace may meet in the middle line, owing to the 



absence of some of the median unpaired series of 



bones; in certain cases the whole of the costals 



thus meeting, owing to the absence of all the 



neural bones. Whereas, in one family of the 



group the plastron contains the same nine bones 



as in the side -necked tortoises, in a second family 



there are eleven bony elements in this part of 



the shell, owing to the presence of an additional 



(mesoplastral) pair between the normal hyo- and 



hypo-plastral bones. 



The side-necked tortoises, of which the great 

 majority may be included in the two families men- 

 tioned above, are all of fresh-water habits, and at 

 the present day are exclusively restricted to the 

 Southern Hemisphere, while they are the only 

 members of the order found in Australia and New 

 Guinea. During the earlier portion of the Tertiary 

 period they extended, however, into the Northern 

 Hemisphere, and in the preceding Secondary period 

 were abundantly represented in Europe. These 

 facts show that the group is a very ancient one ; 

 and by the presence of the additional mesoplastral 

 elements in the lower half of the shell of some 



of its representatives it is allied to a third and totally extinct group, which dis- 

 appeared before the close of the Secondary period. 



Matamata The extraordinary reptile depicted in the accompanying illustra- 



Tortoise. tion, and known as the matamata (Chelys fimbriata), is the typical 

 representative of the first of the existing families of the group Chelyidce. The 

 various genera included therein are collectively characterised by having the normal 

 nine bones in the plastron, by the neck being incapable of complete retraction 

 within the margins of the shell, and the absence of a bony temporal arch to the 

 skull. Eight genera are included in the family, the range of which is restricted to 

 South America, Australia, and New Guinea. 



The matamata, which is an American species inhabiting Guiana and Northern 

 Brazil, and is the sole representative of its genus, is easily recognised by its broad 

 and elongated neck, of which the sides are fringed with peculiar fimbriated pro- 

 jections, and the depressed and triangular head terminating in a proboscis-like 

 nose, and furnished with very small eyes. Not less characteristic is the equally 

 depressed and much corrugated shell, in which the carapace bears three longitudinal 

 ridges, subdivided into nodose protuberances by cross-valleys ; the horny shields of 

 the same being extremely rugose, and marked with deep radiating striae. The 



EIGHT HALF OF THE CARAPACE OF THE 



BLACK STERNOTHERE, WITH 

 HORNY SHIELDS REMOVED. 



THE 



