Vol. XI] CURRAN— REVISION OF THE PIPIZA GROUP 385 



Habitat: New York. Williston, Synop. N. Am. 

 Syrph., p. 291, makes the following remark on this 

 species: "It is not impossible that Chrysogaster apisaon 

 Walker, is the same as this (C. pulchellus). At least 

 the hairy eyes and elongate antennae indicate that it is 

 a Pipiza (Pipizella) or Psilota." 



There is little doubt in my mind but that the above 

 species is one of those described in this paper, but which 

 species it is impossible to tell without an examination 

 of the type. 



Appendix 



Evolution in the Genus Cnemodon 



While it is not intended in this paper to go into the 

 evolution of the genera, it has been found that the genus 

 Cnemodon as limited in the body of this paper, presents 

 many characters of interest to the student of evolution. 

 It seems that this genus is at the present time under- 

 going many modifications in structure. The specimens 

 before me exhibit an exceptionally wide range of charac- 

 ters and it is an easy matter to trace the species through 

 from the most simple form, unicolor, to the more 

 specialized myerma, which is evidently the highest form 

 known. 



C. unicoloY possesses neither the usual slender proces- 

 ses on the middle coxae nor the hind trochanteral 

 processes. It does, however, possess the typically pro- 

 duced middle tibiae, and for this reason is included in 

 the genus Cnemodon. It has also the typical Cnemodon 

 shape, but is closely approached in that by Pipizella 

 frandulenta. From this species the natural step is to 

 C. intermedia, which possesses only the processes on 

 the middle coxae and because of this fact is a species of 

 especial interest. C. cevelata has developed the hind 

 trochanteral processes but, although of the typical 

 shape, they are not as long as in the following species, 

 and are not shortened with the ends rounded, as occurs 

 in the more specialized forms. C. calcarata and 

 elongata are closely related but the latter has the longest 

 processes to be found in the genus. The next step is 



