122 REPORT 108^ U. S. DEPARTMENT OF AGRICULTURE. 



1. No vertical bristles on cephalothorax 2 



A median vertical bristle on cephalothorax Eustathia. 



Two vertical bristles on cephalothorax 8 



2. Ambulacral caroncles flat, circular, almost sessile 3 



Ambulacral caroncles bell shaped, on short peduncles; male without geni- 

 tal disks 6 



3. Abdomen of female not deeply cleft Avenzoaria. 



Abdomen of female deeply cleft 4 



4. Legs III and IV of male subequal in thickness 5 



Leg III thicker than IV; lobes of female abdomen long Allanalges. 



Leg IV thicker than III; lobes of abdomen very short AUoptes. 



5. Abdomen of male enth-e beliind; vulva simply arched ProctophyUodes. 



Abdomen of male cleft behind; vulva more strongly curved, horseshoe- 

 shaped... _ Pterodectes. 



6. Legs, especially the hind pairs, much thicker in male than in female. . Microlichus. 

 Legs not noticeably thicker in male 7 



7. Peduncle of caroncle is placed at tip of tarsi Rivoltxisia. 



Peduncle of caroncle is placed before tip of tarsi Epidermocoptes. 



8. Legs I and II with a spine under one or two joints 9 



No spines on legs I and II 13 



9. Leg III of male without caroncles, tliicker than leg IV Analges. 



Leg III of male with caroncles 10 



10. Leg III of male thicker than IV, with spines on the tarsi Megninia. 



Leg III not tliicker than IV 11 



11. Legs III and IV subequal in thickness, but III longer than IV Protalges. 



Leg IV thicker and longer than III 12 



12. Leg IV of male without caroncle Xolalges. 



Leg IV of male with usual caroncle Analloptes. 



13. Hind legs of male not lengthened nor enlarged 14 



Some of the hind legs larger or longer than anterior legs 19 



14. Legs III and IV short, placed more under the body nearer to the median 



line; front legs of male with processes on some of the joints; body usually 



rather short Freyana. 



Legs III and IV more marginal ; front legs without projections in the male . . 15 



15. Legs I and II of male very much larger and longer than III Falculifer. 



Legs I and II of male not particularly larger or longer than III 16 



16. Leg III of male much thicker than IV 17 



Leg III not much if any tliicker than IV Bdellorhynchus. 



17. Leg IV not noticeably larger than III 18 



Leg IV plainly larger than III Pseudalloptss. 



18. Epimera I in both sexes united to the sternum; genital disks usually 



approximate; tip of abdomen usually entire Thecarihra. 



Epimera I not united to sternum; genital disks usually wide apart; tip of 



abdomen usually bifid Pterolichus. 



19. Leg III of male much thicker than IV 20 



Leg III of male not much tliicker than IV 21 



20. Abdomen of male more or less bilobed at tip; leg III usually reaches behind 



the abdomen, and has no teeth near base Pteronyssus. 



Abdomen of male entire; leg III usually does not reach beyond end of 



abdomen, and has teeth on one of the basal joints Dermoglyphus. 



21. Leg IV without caroncle Xoloptes. 



Leg IV with caroncle Syringohia. 



In Freyana some males have one of the first or second pairs of legs greatly enlarged 

 and elongated for the purpose, it is supposed, of holding the female. Sometimes 

 the enlarged leg is on the right side, sometimes on the left side, and to support it the 

 sternal skeleton is much stronger and differently arranged from that on the opposite 

 Bide of the body, Thjs is the only instance of asymmetry in the family. The hind 

 legs arise nearer the middle of the venter than in other genera, and are very short. 

 Two species have been recorded from this country, one, F. anserina Koch, on the 

 enow goose, and the other, F. caput-medusae Trouessart, on the booby. The latter 

 species is sometimes over 1 mm. long, one of the largest species of the family. In 

 Pterodectes (fig. 258) the body is elongate and slender, the legs aU of about equal 

 development, and in both sexes the tip of the abdomen is bilobed, in the female with 

 two stout bristles. There are distinct shields upon the dorsum. Two species have 

 been found in Canada on various song birds. The genus Allanalges {Pterocolus) is 



