CLASSIFICATION OF ARACHNIDA. 131 



of the labours of Blackwall, published in the Linnaean Trans- 

 actions and the Annals of Philosophy, as well as those of an 

 anonymous writer in one of the numbers of the Magazine of 

 Natural History, from whose admirable pencil and pen, 

 British arachnologists may shortly hope to be furnished 

 with a most invaluable series of memoirs. 



The class, as at present constituted, has generally been 

 divided into two orders the pulmonary and the- trachean 

 Arachnida : but, in his last work, Latreille has established a 

 third order, Aporobranchia, for a very remarkable group of 

 animals, which Leach regarded as possessing so doubtful a 

 situation, that in the Entomologists' Compendium they were 

 placed at the end of the true insects. 



The class may therefore be thus distributed : 



SECTION I. PULMONARIA. 



Having pulmonary sacs for respiration, with six or eight 

 simple eyes : consisting of two orders. 



ORDER I. 



The Dimerosomata of Leach, or the Araneides of Latreille, 

 consisting of the great group of spiders, divisible into various 

 families, having the abdomen attached by a footstalk, and 

 not articulated. 



ORDER II. 



The Polymerosomata of Leach, or the Pedipalpi of Latreille, 

 consisting of the scorpions, and divisible into two families, 

 Scorpionida and Phrynidce, having the abdomen attached by 

 its whole breadth, and composed of numerous segments. 



SECTION II. TRACHEARIA. 



Having tracheae for respiration, never with more than four 

 eyes : consisting of two orders. 



ORDER III. 



Adelarthrosomata, or those trachean species which have 

 the mouth furnished with visible didactyle chelicera, and the 

 abdomen annulated, although occasionally in an indistinct 

 manner. 



