Tertiary Spiders and Opilionids. 227 



Sub-Order Arachnomorph^. 



Spiders with an iinsegmented abdomen and a single pair of 

 lungs. Usually a single median tracheal spiracle in front of the 

 spinnerets, sometimes a pair of them. Articulation of chelicerae 

 such that the fangs move in a plane intersecting the plane of 

 symmetry. 



This sub-order can be naturally divided into two divisions : 



I Division Cribellat^. 



True spiders with a cribellum in front of the spinnerets and a 

 calamistrum on the fourth metatarsi. 



Eight recent families belong to this division. Some of the 

 species are exceedingly common. There are however no repre- 

 sentatives of Cribellated spiders among the Tertiary spiders of 

 North America. 



2 Division Ecribellat^. 



True spiders without a cribellum or calamistrum. This division 

 comprises 28 families of recent spiders. We shall mention only 

 those families with which the Tertiary spiders are more or less 

 directly concerned. 



I SuB-DlVISION HaPLOGYN/E. 



This sub-division comprises six families of spiders in which the 

 external genital organs are comparatively simple in structure and 

 resemble those in Theraphosid spiders. Three of the six fami- 

 lies, namely Oonopidse, Dysderidse and Caponiidse, have two pairs 

 of spiracles on the abdomen. In the Caponiidse both pairs lead 

 into tracheal tubes. In the Oonopidse and Dysderidse the first 

 pair leads into lung-books, the second into tracheal tubes. In the 

 remaining three families, namely Sicariidae, Leptonetidse and 

 Hadrotarsid^e the spiracles are distributed so that a pair of them 

 belongs to the lung-books, and a single median spiracle leads into 

 the tracheal tubes. 



The Caponiidse have eight eyes, the Oonopidse and Dysderidse 

 have six eyes. The Dysderidse have a colulus in front of the 

 spinnerets, the Oonopidse have none. 



