2 TERTIAKY RH VNCHOPHOROTTS OOLEOPTERA. 



marked as to-day, and the triuiig'ulin larva of Meloe has lieen found in- 

 chised in amber, showinji' that the ))henonienon of hypermetamorphisni had 

 ah'cady been developed. 



The hisects of the Tertiary period, therefore, afford no such interestincr 

 series as may be found in the study of Tertiary mammalia, nor as eau he 

 found in the study of the insects themselves in Paleozoic rocks. Never- 

 theless, a few interesting features have been pointed out which seem to 

 stand, in some measure, as exceptions to what has been stated. Thus, in 

 my recent work on our Tertiary insects,^ I called attention to some remarka- 

 l)le features in the fossil ])lant-lice of our Tertiaries, especially the great 

 lensrth and slenderness of the stigmatic cell — a feature which affects the 

 whole to])ograpll^' of the wing, and is found also in the only 3Iesozoic plant- 

 louse known, Ijut which, nevertheless, can not be regarded as of significant 

 taxonomic importance, since it occurs equally in both the A[)hidin;v and 

 Schizoneurina', the two principal subfamilies of that group, l)oth to-day and 

 formerly. 80, too, in treating in the same place of the Pentatomida?, I 

 pointed out tliat the scutellum was universally shorter in all our Tertiary 

 forms, whether belonghig to the sul)family of Cydnin;e or Pentatomina'. T 

 may further add the uniniblished fact that it is a peculiarity of the Tertiary 

 Staphylinida- of this country that the antenna- ;uid legs are measurably 

 shorter than in modern types; this is most marked in cases where the living 

 and extinct species of the same genera are compared. But in neither of 

 these cases, any more than in the Aphidae, can we regard these peculiari- 

 ties as any ground for separating the fossil from the recent forms as distinct 

 groups. No doubt we shall some day be ai)le to correlate these differences 

 and point out their precise significance, which at present is not clear, but it 

 is certain that they do not afford ground for maintaining that we are here 

 dealing with extinct groups any higher than genera, or, at most, than tribes. 



Yet in one or two instances extinct groups of a higher grade may 

 be found. Thus, in the work already alluded to, and previously, I have 

 drawn attention to a strange ty])e of fossil Thysanura — Planocephalus — 

 for which it seemed necessary to frame a new suborder, and, though its 



' Tertiary Insects of North America, Reports U. S. Geological Survey of the Territories, Vol. xiil, 

 4", 1890.' 



