1915] On Proper Generic Concepts 89 
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Sisyropa hemerecampoe Twns. Cnephalomyic floridana Twns 
; Lyorista eudryce Threc Twns) ' 
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; Lumosicera coccidella Tuns. 
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Exoristid Masiceratid 
EXPLANATION OF DIAGRAM. 
The diverging lines from the two conimon points represent generic stems 
including typical species or those of same general type as the stems. Branch lines 
from the stems represent atypical or transitional species which must be grouped 
with those restricted genera in common with which they show a preponderance 
of important characters. 
The portion of diverging lines below horizontal dividing line represents young 
stocks; the portion above same, old stocks. As stocks age the generic stems 
become farther removed from each other, and transitional species largely drop out. 
Cnephalomyia floridana and Pseudogonia ruficauda are generically distinct 
forms, within the Spallanzaniine tribe, with greatly contrasted egg and first-stage 
maggot, yet so alike in adult as to be almost indistinguishable. Very slight but 
constant head characters separate them, and the early-stage characters show that 
the value of these slight adult characters is generic. 
Eumasicera coccidella is a Masiceratid whose adult is extremely similar in 
external anatomical characters to the adults of the Exoristids Sisyropa hemero- 
campe and Exorista eudrye Thompson (nec Townsend), yet the first possesses 
microtype eggs while the others possess elongate sub-cylindrical macrotype eggs 
with short pedicel. All would be referred to same genus on external adult charac- 
ters, but the small differences in latter are shown by the early stages to be of 
family value. 
While the diagram might be taken to indicate convergence in the adults in 
these two cases, it is intended merely to illustrate the close similarity in external 
adult characters of forms shown by early stages to be ver, distinct. The actual 
descent has probably been through adult parallelism in both these cases, with 
juvenile divergence in the Spallanzaniine case, and juvenile-reproductive diver- 
gence in the Masiceratid-Exoristid case. 
