RISE AND PROGRESS OF ZOOLOGY. IxV 



absence or presence of tail, from a shelly co- 

 vering, from the absence or presence of teeth, 

 from being furnished with lungs ; number, situ- 

 ation, and figure of the scuta or scales ; num- 

 ber and situation of spiracula, fyc. %c. 



In the order of Reptiles the specific cha- 

 racters of the Testudo genus are deduced prin- 

 cipally from the difference in the shells and 

 feet ; in the Lacerta from the head, tail, toes, 

 and various other parts ; in the Roma from the 

 diversity in the make of the body, and from the 

 number of claws and the hind and fore-feet. 

 The specific characters of the Serpentes were 

 more difficult to ascertain. Linnaeus used the 

 number of the small shields and scales, or the 

 rings and rugae of the belly and tail, and the 

 proportion these bear to each other in the differ- 

 ent species. But this character is liable to 

 great uncertainty. The pattern or general dis- 

 tribution of markings in each species is more 

 constant, and has been more dwelt upon by the 

 followers of Linnaeus. 



Linnaeus originally included two more orders 

 in this class, the Meantes, solely made for the 

 genus Siren, and that of Nantes, which are 

 fishes, and breathe by gills. His successors 

 have excluded them. 



The fourth Class, Pisces, is subdivided into 



