1900.] GROTE—THE DESCENT OF THE PIERIDS. on 
and #2 spring from radius before cross-vein, MVeophasia agrees 
with the more specialized Perrhyéris. 
Gen. Perrhybris Hiibn., 1816. 
Dype= PB. pyrrha. 
Perrhybris pyrrha. 
Wings ample. Radius three-branched; Ar and 2 in origi- 
nal position above the discal cell; cell closed, upper half of vein 
between 472 and 473 shrunken, the shorter vein between J/2 and 
radius strong and showing a central backward projection, the 
remnant of the base of the median system. Second anal vein with 
a slender fork at base. Hind wings with humeral spur strongly 
turned outwardly ; cell closed, vein between 4/2 and 173 somewhat 
shrunken ; a single very slight backward projection on cross-vein 
between J7/2 and radius; subcostal vein apparently solid at base. 
The correspondence in the neuration between Pyrrhydris and 
Mancipium or Pontia may, I think, be due to convergence ; other- 
wise we should have to regard the former as a specialized Pverzs, of 
very strange pattern of ornamentation: ‘The stage to which Pyrr- 
hyéris has attained in the reduction of the radius is anticipatory of 
Delias, but the relationship cannot be considered as direct or an- 
cestral, since the reduction of the media is less advanced in De“as. 
If it were not for the existence of the latter genus, which is clearly 
ancestral to Prccarda, we might regard Pyrrhyéris as a very early 
forerunner of the latter. As it is, the line Prccarda-Delias has 
probably emerged from the direct line of Pzer7s, from forms in 
which the median branches still kept to the cross-vein. The gen- 
eral directions in the reduction of the radial and median branches 
has been pointed out, and these studies now show the inequality in 
the rate of specialization between the two systems. In establishing 
phylogenetic lines we have to reckon with all the factors; in the 
present paper I am mainly endeavoring to show how the neurational 
features may be used, as well as the difficulties they present. I 
hope to have made it plain that their value is very great, but this 
will come out more clearly the more material is examined and com- 
pared. 
In pattern of ornamentation Pyrrhydris is dimorphic, and the 
white color of the male above may be considered historically more 
recent and a specialization. But, in the veining, the sexes are 
