56 FOSSIL BUTTERFLIES. 



three-fifths of the lower median interspace, where it does not occur in P. Protn- 

 i/iw; and this affords the principal ground for supposing the insect to be generi- 

 c-ally distinct from Pontia, no distinctive premarginal spot occurring in this inter- 

 space in any species of Pontia which we have seen. The dusky premarginal 

 fleckings of the nervures terminating on the outer border, often enlarging into 

 distinct spots, which are so usual in Pontia, especially in the upper half of the 

 wing, are also absent from the fossil species; but in their place the whole outer 

 margin appears to be almost uniformly, though not heavily, griseous, a little more 

 distinctly so in the upper than in the lower half of the wing. The spot just 

 beyond the middle of the medio-submedian interspace, distinct in P. Protodice, 

 but deepest in shade on the lower half of the interspace, and in other species 

 sometimes wholly confined to it, is seen in the fossil species, but is far less 

 distinct, confined to the lower half and situated exactly in the middle. There 

 are indications also of dark markings following the basal third of the sub- 

 median nervure; and apparently the basal half of the costal edge, as far as the 

 costal nervure, is darker than any part of the wing, excepting in a sudden and 

 rather broad, distinct break in its middle. This darker portion is considered by 

 Heer as the femur of one of the legs, superimposed upon the base of the wing; 

 perhaps, however, this is due to an accidental folding of the wing at this point, 

 which seems the more probable, because if we suppose this darker portion to be 

 turned back, the curve of the costal border would approximate much more closely 

 to its condition in P. Protodice; while its present form is much straighter, exhib- 

 iting only a very slight and regular convexity. As far as can be judged from 

 the fragment, the form of the other parts of the wing coincides with that of P. 

 Protodice. 



As in all species of Pontia there is a slight wrinkling of the membrane in the 

 interspaces, forming slight channels running from the outer border inward, nearly 

 to the depth of two interspaces, indicated in the fossil by dark lines as heavy as 

 the nervures, and caused by their filling with sedimentary material. The extreme 

 length il the part of the wing preserved is 24"""' and the greatest width 22.5" 1I1K . 



The markings lead one to conjecture that the individual was a male. 



