220 Journal New York Entomological Society. CVoi. xxi. 



pearance in print. It will at least serve to unify our present knowledge 

 of this series of important groups. 



The species discussed in this paper are those grouped in the Agro- 

 myzidse and Geomyzidse of Williston's Manual. These small flies be- 

 long to that division of the Acalyptrate Muscidae where the auxiliary 

 vein is more or less rudimentary, ending, together with the first longi- 

 tudinal vein,* distinctly before the middle of the wing; the basal cells 

 small and manifesting a tendency toward becoming incomplete, but 

 the anal cell almost always formed, although never produced. The 

 head is spherical or hemispherical, conical only in Selachops; is schizo- 

 metopic, which means that the frontal orbits are continuous with the 

 facial orbits and with the genae; the orbital bristles descend to below 

 the middle of the front; the center of the face is usually depressed 

 below the level of the orbits, and is not large nor arched, protuberant 

 only in Sinophthalmus ; the arista is rarely loosely and long plumose, 

 is usually quite bare, but ranges to long-pubescent or even plumose; 

 the scutellum has protuberances only in Rhodesiella; the posthumeral 

 bristle is regularly absent; the legs are never greatly lengthened and 

 very rarely thickened ; the tarsi are always slender, with the metatarsus 

 the longest joint. The oral vibrissae may be present or absent, the 

 wings may be pictured or not, the body may be stout or rather slender ; 

 the color may be dark or light, and the proboscis may be long or short. 

 The vestiture may consist of a dense pruinosity or the insect may be 

 highly polished, while the body may have many or few bristles, or may 

 be clothed with hairs. 



While the limits of the combined group here discussed are rela- 

 tively easily fixed, there being but few genera that have been ques- 

 tioned,^ it has not proved so easy to define the boundaries of the sub- 

 families within the group. Various writers have reassigned doubtful 

 genera here and there, as will be seen in their discussion at the close 

 of this introduction. 



Hendel and Czerny, recognizing the importance in phylogeny of 

 hidden characters that have not been influenced by the mode of life 

 of the species, have proposed the most satisfactory outlines of the sub- 

 family limits, emphasizing such apparently trivial but ancestral char- 



1 SiUgo Aldrich was described as a Helomyzid ; Pelomyia Williston as an 

 Ephydrid ; Eusiphona Coquillett as a Tachinid ; Lestophonus Williston as an 

 Oscinid. 



