36 



S. H. SCUDDER ON PALAEOZOIC COCKROACHES. 



Shaler, with some of the later coal deposits of the eastern border region ; but assuming 

 the millstone grit of the east and west to be of the same age, we may express tolerably 

 well the general stratigraphical relations of the species by the following table : 



If we assume the separation between the upper and middle carboniferous to be correct, 

 we shall have the following percentage of the species from the different formations in either 

 country : 



In Europe : Above the upper carboniferous 26 per cent. ; in it 74 per cent. ; below it 7 per cent. 



In America: Above the upper carboniferous 6 per cent.; in it 24 per cent.; below it 76 per cent. 



Certain species appearing in the lists twice over make the totals of percentage in each 

 case above 100. It would appear from this summary that the American cockroaches are 

 the older, and a certain light is thus thrown upon the occurrence of Mylacridae in the New 

 World only. 



I have already given some reasons for believing, not only that cockroaches formed the 

 majority of insects in palaeozoic times, but that the actual number of species was very 

 great. That they were also abundant in individuals is probable, judging from the present 

 fecundity of their descendants and from a few other facts. Goldenberg, for instance, re- 

 marks (Faun. Saraep. foss. I, 17) that where one finds any remains of cockroaches in' the 

 palaeozoic rocks, one nearly always discovers more than a single fragment ; at least this was 

 the case with Etoblattina primaeva, E. labachensis and Blattina Tischbeini ; and he 

 judges from this, that, as at the present time, these creatures collected in numbers in a 

 single spot ; but it seems rather to indicate merely the great numbers of individuals which 

 then existed. Goldenberg elsewhere remarks (Faun. Saraep. foss. II, 21) that cockroaches 

 formed nearly one-half the insects of the coal period, reaching then their greatest develop- 

 ment. He finds reasons for this, first, in the warmth and obscurity of the forest vegetation 

 of that time, which only suited such animals as these ; and second, in the intimate corre- 



