24 Trans. Acad. Sci. of St. Louis. 



HARPYEHYXCHUS Meg. 

 H. longipilus Banks — Loxia curvirostra minor (Brehm.). 

 H. nidulans Megnin— Alauda arvensis Linn., also en grosbeak sp. (?) 

 H. brevis Ev/ing — Coccothraustes vespertina (Coop.). 



The parasitic members of the Cheyletidae form a very- 

 small and probably heterogeneous group. The five dif- 

 ferent genera are morphologically rather widely sepa- 

 rated and each is markedly specialized. These genera 

 are certainly not in the least allied to the atracheate 

 parasitic forms which in all probability arose from atra- 

 cheate free-living types. For the present, on account of 

 convenience, we will consider them taken together as a 

 group. 



Two of the genera Myohia and Psorergates are found 

 on mammals, the former attached by their highly spe- 

 cialized clasper-legs to the bases of the hairs, the latter 

 in little cavities or cells just beneath the skin. Two of 

 the other genera, Picobia and Syringopliilus, live inside 

 of the quills of the feathers of birds; while the genus 

 Harpyrhynchus is found forming tumors in the skins 

 of birds. 



Of the thirteen species known in this group all are 

 confined either to a single host species or to very closely 

 related host species. These extremely narrow limits in 

 their distribution are due chiefly to one of two things; 

 either the development of a highly specialized clinging 

 apparatus or to semi-endocolous habits. Thus the mem- 

 bers of Myohia have the highly specialized claspers for 

 grasping a single hair; and it would be impossible for 

 them to hold on to a hair very much smaller or very 

 much larger than those of their host. 



Of course the members of the genera Picobia and 

 Syringopliilus, living inside the quills of birds, would 

 have only rare chances for their transference from one 

 host to another. Likewise the members of Psorergates 

 and Ilarpyrliynclius which are almost endocolous would 

 not be easily transferred from one host to another. 



