ORDER POLYMEROSOMATA. 143 



gether,) and comprising the families of Mygalidas (the gi- 

 gantic bird spiders, as they have been erroneously termed, of 

 tropical countries), Atypidae, and Dysderidce. 



Section 2. Dipneumones, or those which have only two 

 pulmonary sacs and two external spiracles, comprising the 

 majority of the order, and divisible, according to the man- 

 ner of construction of the web, into the families Araneidce, 

 which spin irregular webs having a cylindrical cell in one 

 corner; Theridionidce, comprising sedentary species which 

 make an irregular web without any tubular retreat ; Epei- 

 ridce, which weave geometric webs ; Thomisida, hunting 

 spiders, possessing the power of walking sideways ; Ly- 

 cosidee, wandering spiders, catching their prey whilst walking 

 about, and not making a web, except for the reception of 

 the egg ; and lastly, the Salticidte, differing from the latter 

 in the agility with which they leap upon their prey from a 

 considerable distance. 



ORDER II. POLYMEROSOMATA. 



This order is distinguished by having the abdomen at- 

 tached by its entire breadth to the thorax, and composed 

 of numerous distinct segments. It consists of two fami- 

 families, the Scorpionidts and Phrynidce, in the first of which 

 the thorax is furnished on the under side with two moveable 

 comb-like plates, and terminated by an elongated and knotted 

 tail, the extremity of which is armed with a curved and very 

 acute sting. The breathing pores are eight in number, ar- 

 ranged four on each side along the belly ; the arms (or palpi, 

 very greatly developed) are of very large size, serving as in- 

 struments of prehension, and terminated by a large claw. 

 The legs are eight in number, of moderate size, and much 

 larger than the palpi. The eyes are eight in number, three 

 on each side of the thorax, and two on the back. The " an- 

 tennae-pincers" are terminated by two fingers, one of which 



