98 



ARTHROPOD A. 



species from the Coal-measures of Illinois, appears to have had a 

 segmented abdomen. 



Spiders are oviparous, generally placing their eggs in a silky 

 cocoon, which is sometimes carried by the mother beneath the 

 body. Species of Cteniza, Atypus, and other genera construct 

 tubular burrows, lined with silk or otherwise, and closed with a 

 hinged door. These are the ' ' trap-door spiders." Gossamer is 

 the web formed by young spiders, by which they are enabled to 

 float to a great height in the air. 



Argyroneta aquatica is the well-known water-spider ; the house- 

 spider is Teyenaria domestica. The " bird-spider " (My gale aviwi- 

 laria) is strong enough to kill small birds. 



Spiders have been divided into two groups dependent on the 

 number of pulmonary sacs [Dipneuinones with two, Tetrapneu- 

 mones with four] ; also on the number of eyes [two, six, or 

 eight]. Only one is known with two eyes, Nops guandbacoce, a 

 Cuban spider ; three or four have four eyes. The species with 

 two pulmonary sacs, the great bulk of the order, have been formed 

 into two divisions, Sedentariae and Vagabundap, the former again 

 divided into Orbitelariae or Inaequitalae, Ketetelariae, Tubitelaria?, 

 and Laterigradae ; the latter into Citigradje and Saltigradas ; while 

 the species with four pulmonary sacs comprise only one division, 

 Territelariae. These divisions, however, dependent chiefly upon 

 habits, form of the web, &c., seem incapable of being satisfac- 

 torily defined ; and accordingly they have only been indicated in 

 the following list, in which Thorell's arrangement has been gene- 

 rally adopted. Recently Bertkau proposes to divide spiders ac- 

 cording to the number of spiracles : Tetrasticta with two pairs, 

 Tristicta with one pair ; the latter including all the families 

 except " Atypidae " and Dysderidse. 



According to Cambridge, there are about 500 British species of 

 spiders. 



Gastracanthidce. 

 Gastracantha. 

 Acrosoma. 

 Cyrtarachne. 



ORBITELARI.E. 

 Epeiridce. 



Tetragnatha. 



Epeira. 



Argyope. 



Nephila. 



Miagrammopes. 



Uloborus=Veleda. 



Phoroncidia. 



Arcyidce. 

 Arcys. 

 *Archsea. 



Poltys. 



RETETELARLE. 



Theridiidce. 

 Theridion. 

 Neriene. 

 *Mizalia. 

 Erigone. 

 Walckenaera. 

 Linyphia. 

 Argyrodes. 

 Tapinopa. 

 Steatoda. 



