PARKER: NEW ENGLAND SARCOPHAGIDAE. 31 
Basis of un)ii|)in^': /'(/■ i.rtrnial rh(tr(icf<r,s, fourth rcninil phtirs, 
forceps. 
Specific characters: luoM vxicriial churdctcrs, penes. 
(ironp e. 
Isolated species showing' no distinct relationship. 
The genus Sarcophaga, then, is niiide up of isolated species and 
species groups, some natural, some perhaj)s artificial and containing 
heterogeneous forms. By listing these groups as above several facts 
are made apparent, which may seem self evident: (1) that though 
each group is defined by characters common to all its species, yet no 
two groups are defined by the same set of characters; (2) that no 
individual character of a group is likely to be peculiar to that group 
alone but may appear in one or more other groups combined with a 
dift'erent set of characters. A group therefore cannot be defined by 
one character alone but by a combination of characters. (3) That 
since the same set of characters appears in no two groups, the total 
number of dift'erent characters represented by all the groups is greater 
than that of any one group. The total number of different characters 
then, are the specific characters of the genus, and within any group 
those not common to all its species become the ones by which these 
are separated. 
Applying the same method of procedure to the other two genera 
considered we have the following result. 
Ravinia. — The species of this genus have more characters in com- 
mon than do those of Sarcophaga, that is, a greater number that are 
of generic value. These characters include a portion of those which 
were generic in Sarcophaga and a portion of those that were specific. 
The color of the epaulets, for instance, is specific in the latter but 
generic in Ravinia. External characters of species within the two 
groups indicated in that part of the genus represented in this paper, 
are fully as distinct as those of the penes, sometimes more so. 
Basis of genus: matiy external characters, similar claspers, parts of 
penes easily homoJogized, similar forceps. 
Basis of groups: few external characters, similar penes, similar fourth 
ventral plates. 
Specific characters: few external characters, penes. 
Bocttcheria. — In general the same remarks apply to this genus as to 
Ravinia. Its species, however, are very similar in every way. 
