S. H. Scudder—Rocky Mountain Triassic Insects. 201 
Fairplay (i.e. those which do not belong to the Paleoblattaris) 
is less than 8°5, ranging from 6°5-115™™. This agrees co 
pletely with the size of Mesozoic species already known. The 
average of all the Fairplay cockroaches is less than 13°5™™. 
s to the six cockroaches from Fairplay which do not belong 
to the Paleoblattariz, the characteristics of their venation, as 
well as their smal] size, show them to be closely allied to 
Jurassic forms, although the three or four genera to which they . 
belong are distinct from any yet characterized. Two of them 
are distinctly allied to Rithma, a genus established rather loosely 
by Geibel for some species from the English Purbecks figured 
by Westwood. 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 these 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 Paleoblattariz excepting some of those 
mentioned above from the same Fairpiay 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 Paleozoic to Mesozoic 
forms has taken place, and does not bear out the suggestion 
made in my memoir on Paleozoic cockroaches (based on a 
Comparison of the venation of the front and hind wings of 
