No. 2303. jtED SPIDFrf^ OF AMERICA— ^f(■GREOOR. 649 



Genus TETRANYCHUS Dufour. 



Tetninychus Dufour, 1832, Ann. Sci. Nat., vol. 25, p. 276. 



Until quite recently there were included under this generic name 

 practically all the red spiders or spinning mites. As designated by 

 the most recent workers, however, there are included in this genus only 

 those species in which the empodial claw is divided into from four to 

 six subequal divisions. Based on this new conception of the genus 

 there are in Europe three or four species and in America about ten 

 species. With respect to the tarsal, palpal, and collar trachea char- 

 acters, there is rather good coordination among the several species of 

 Tetranychus; on the other hand, the penis exhibits rather radical 

 variation within the genus. With a very few exceptions the more 

 important red spiders economically are contained within this genus. 



Red spiders the empodial appendage of which is cleft to the middle 

 or more with from four to six subequal divisions, the whole strongly 

 bent near middle; collar trachea V-shaped, of about the same caliber 

 throughout. 



Type — TetrQ,nychus telarius Linnaeus, designated by Trag&rdh, 

 1915. 



KEY TO SPKCIES OF THE GENUS TETEANYCHU.S. 



1. Empodial appendage lour-cleft 2 



Empodial appendage more than four-cleft 3 



2. Penis slender; basilar lobe obtusely sharp-angled; shaft slender, strongly hooked , 



acuminate without barb T. telarius Linnaeus. 



Penis shaft rather broad, with a small protuberance on the concave side, weakly 

 hooked and blunt pointed; male tareus with three-cleft empodial claw; collar 

 trachea U-shaped, anterior arm twice as long but of same caliber as posterior 



arm T. olthaeae Von Hanstein. 



Penis much broader; basilar lobe in the form of a broad rectangular projection; 

 shaft rather stout, weakly hooked, Mdth a tnincate pseudo-barbed tip. 



T. ludeni Zacher. 

 .3. Empodial appendage five -cleft; penis somewhat undulate, sting-like, unbarbed, 



T. Jlavus Ewing. 

 Empodial appendage six-cleft 4 



4. Empodial appendage six-cleft, tip of tarsi broad, truncate, each bearing very long 



tactile seta; palpal "thumb'" with at least 5 digituli near tip. 



T. inultidigituli Ewing. 



Empodial appendage six-cleft, tarsus narrowed toward tip, palpal "thumb" 



with only two digituli near tip 5 



5. Penis shaft tapeiing without well-defined hook 7 



Penis shaft stouter v^dth well-defined hook 6 



6. Collar trachea U-shaped; penis vrith. small, hooklike dorsal basilar lobe, and stout 



upturned hook bearing recurved barb T. himaculatris Harvey. 



Collar trachea V-shaped; penis with prominent dorsal basilar lobe, and sti-ong 

 upturned hook bearing a barb, the posterior tip of which is produced into a 

 long, sharp spur T. pacijicus, new species. 



7. Tip of penis with knoblike barb, basilar lobe about equal to inner lobe in length. 



T. borealis Ewing. 



