THE CANADIAN ENTOMOLOGIST. 89 



these are the radial furrows ; the region of the cephalothorax between 

 the anterior pair and embracing the eye region is called the head or pars 

 cephalica. The mandibles are the anterior pair of mouth-parts ; they are 

 two-jointed, the second joint being called the fang, and furnished with the 

 opening of the poison gland. The maxillae form the second pair of 

 mouth-parts ; to the sides of the maxillae are attached the palpi, which in 

 the adult male have the terminal joint peculiarly modified for sexual 

 purposes. Between the maxillas and articulated to the sternum is the lip. 

 The sternum is the ventral plate of the cephalothorax, the entire region 

 between the base of the legs. The legs, of four pairs, are numbered from 

 before backward, I., II., etc. The legs are seven-jointed ; the joints are 

 called, beginning at the most basal, coxa, trochanter, femur, patella, tibia, 

 metatarsus, and tarsus ; in a few peculiar groups there is an eight joint, 

 the onychium. At the end of the tarsus, or onychium if present, are two 

 claws, equal in size ; below and between them is frequently a third, smaller 

 and more curved. The claws may be furnished with teeth, and are called 

 dentated. Sometimes under the two larger claws, in place of a third, is 

 a dense brush of hairs called a scopula. The abdomen is joined to the 

 cephalothorax by a slender pedicel. At, or near, its extremity on the 

 under side or venter are the spinning organs called spinnerets ; these are 

 of three pairs, the middle pair smaller and concealed by the other two. 

 The spinnerets are probably always two-jointed, but in some spiders one 

 pair is very prominently so. At the base of the lower pair of spinnerets 

 is sometimes a transverse surface provided with spinning tubes ; this is 

 called the cribellum. Complementary to this in function is a row of stiff 

 hairs or bristles on the posterior metatarsi called the calamistrum. Near 

 the base of the spinnerets is a pair of stigmata, which are sometimes 

 placed much more anteriorly, even nearer the basal than the distal end of 

 the abdomen. When so situated there is formed a transverse ridge or fold 

 on the venter. Near the base of the venter is a pair of transverse slits ; 

 these are the lung-slits. In some spiders there are two pairs. Between 

 them on the median line is the opening of the genital organs ; in the 

 female called the epigynum. Its structure, together with the structure of 

 the male palpal organ, is of utmost importance in the determination of 

 species. 



Because of certain peculiarities, I shall treat the cave forms separately 

 in the key. The characters of the families as indicated in the system 

 should be used in connection with the key. 



