THE ACAEIXA OR MITES. 



33 



Parthenogenesis has been claimed for several species of Tetranychus. 



Several authors (Megnin. Kramer, Triigardh) have kept the Tetranychidae separate 

 from the Raphignathidse, since in the latter family the abdomen is more or less dis- 

 tinctly divided into segments, but this seems hardly advisable, considering the 

 variation and indistinctness of the 

 segmentation. The more promi- 

 nent genera are distinguished in 

 the following table: 



1. Tarsi (at least tarsus I) 



much shorter than 

 the preceding joint; 

 at least leg I as long 



I as, or longer than 



I body 2 



Tarsi as long as preced- 

 ing joint; leg I rare- 

 ly as long as body . 



2. Front margin of cepha- 



lothorax with a thin 

 four-lobed or cleft 

 plate; body with 



scalelike hairs Bryohia 



No such plate on front 

 of body 



3. Body with simple 



hairs; prostigmaina 



horn each side at base of mandibles Tetranohia. 



Body with spines or stiff serrate bristles; prostigma not in a horn 4 



4. Tarsi I enlarged a little near tip; palpi stout Tetrany china. 



Tarsi I tapering to tip; palpi small and slender; coxae close together. Neophyllobius. 

 Dorsal surface divided into many small areas; claws two, very \2iTge..Raphignathus. 



5 



Fig. 40. — Tetranychus, cephalothorax from above: a, Palpus; 

 h, mandibular plate; c, frontal bristle; d, subfrontal bristle; 

 c, eyes. (Author's illustration.) 



Dorsal surface not so divided. 



6. Palpi very slender, arid not 

 showing plainly the claw 

 and thumb arrangement; 

 mandibles not elbowed 

 near base 7 



Palj^i stouter, showing 

 plainly the claw and 

 thumb arrangement 8 



7 . Legs transversely wrinkled ; 

 large, bordered ventral 

 apertures; eyes present 

 Tenuipalpus. 



Legs not transversely wrin- 

 kled; ventral apertures 

 smaller; eyes indistinct 

 Tetrany choides. 



8. Prostigma in a horn each 



side at base of mandibles; 



body short and broad, with large prominent spines above Tetrany chopsis. 



Prostigma not in a horn, or else body not with spines 9 



9. Mandibles styliform, elbowed near base; and with a supramandibular 

 plate; body not elongate, and thumb not extending much beyond 



claw Tetranychus. 



Mandibles less styliform, not elbowed near base ; no supramandibular plate . 10 



10. Coxae close together, body rather short Acheles. 



Coxae in two well-separated groups; body elongate 11 



11. Thumb extending much beyond the claw Caligonus. 



Thumb barely extending beyond claw Sligmaeus. 



Fig. Al.—TctranycliuSjlQg: a, Coxa; 6, trochanter; c, femur; 

 d, patella; c, tibia;/, tarsus: g, onychium; ft, claws. (Au- 

 thor's illustration.) 



