from tlte Rochy Mountains. 257 



which they belong avc distinct from any yet characterized. 

 Two of them are distinctly allied to Eitauia, a genus 

 established rather loosely by Giebel for some species from 

 the English Purbecks figured by Westvvood. They all have 

 a decided Mesozoic aspect, and would at once be considered 

 Liassic, or at least Jurassic, by any one familiar with the 

 forms already known from those deposits. They have, on 

 the other hand, an entirely different aspect from any and all 

 Paleozoic forms, and present no points of close comparison 

 with any Pala^oblattarire, excepting some of those mentioned 

 above from the same Fairplay beds, notably with the genus 

 mentioned under the name of Poroblattina, which one of the 

 genera not a little resembles. 



This resemblance is of special interest because it points out 

 the method in which the change from Palaeozoic to Mesozoic 

 forms has taken place, and does not bear out the suggestion 

 made in my memoir on Palaeozoic cockroaches (based on a 

 comparison of the venation of the front and hind wings of 

 existing cockroaches), that the scapular and externomedian 

 were the two veins wiiich were amalgamated in the historical 

 development of the group. For when we compare the series 

 of genera near tiie boundary line of the departure of the 

 Pala^obhaltariai towards later forms (those Palaeozoic cock- 

 roaches allied to Petnihlattina)^ and especially those brought 

 to light by the discoveries at Fairplay, we find that, in the 

 Mesozoic species at least, it is the mediastinal and not the 

 externomedian vein which has blended with the scapular, 

 although the externomedian also may become blended with 

 the others in living types. This amalgamation has proceeded 

 by the enlargement of the scapular area, which has crowded 

 the mediastinal towards the base of the wing, whose few 

 remaining branches finally become attached to the scapular 

 vein, no trace of their former dependence remaining visible. 



We have then at Fairplay an assemblage of forms alto- 

 gether different from anything hitherto found in the Palaeo- 

 zoic series on tlie one hand, or in the Jurassic beds on the 

 other. They show a commingling of strictly Jurassic forms 

 with a larger proportion of types which may be called Upper 

 Carboniferous or Permian with a distinct Jurassic leaning. 

 There is therefore a strong probability that the beds in 

 which they occur belong to the intermediate formation, the 

 Triassic. 



If this should be proved, Mr. Lake's discovery will have 

 an added interest, from the fact that almost nothing is known 

 either of the plants or of the insects of this formation. Of 

 the plants, it is only necessary to point out that in the 



Ann. & Mag. N. Hist. Ser. 5. Vol. xiv. 20 



