440 SAMUEL II. SCUDDER ON 



As in the paleozoic cockroaches, so here, most of the remains consist exclusively of 

 fronl wings, and the principal guide to our knowledge of these early forms comes nec- 

 essarily from a study of the neuration of these parts. This study, in the case of the 

 paleozoic cockroaches, led to the discovery of some features of fundamental importance, 

 by which the front wings of paleozoic cockroaches could be invariably distinguished from 

 those of existing types. In p deozoic forms all of the main veins are completely inde- 

 pendent, and the anal nervules fall at regular intervals upon the inner margin. In exist- 

 ing types, two or more of the main veins are amalgamated, either completely or to a large 

 extent, while the nervnles of the anal area strike the anal furrow, or at least compose a 

 fusiform bunch directed toward the tip of the furrow. In consequence of these distinc- 

 tions the paleozoic forms were distinguished as a separate group under the name Palaeo- 

 blattariae. 



This discovery naturally led to the enquiry: Which of the veins in the modern tcg- 

 mina have undergone the blending process? An examination of existing species showed 

 that, as a rule, the veins were still independent in the hind wings, and an opportunity was 

 therefore afforded of investigating the subject by the comparison of the front and hind 

 wings of many modern types, and the conclusion reached that in modern tegmina the 

 scapular and externomedian veins were those which had blended. 1 



This conclusion was shortly shown to be incorrect for mesozoic types, by the discovery, 

 above mentioned, of cockroaches in the Triassic beds of Colorado, where a series of forms 

 were found associated, some of them belonging to the Palaeoblattariae, and some with 

 blended veins, allowing a more exact comparison than had before been possible. The 

 conclusion newly reached from their study was that "when w T e compare the series of gen- 

 era near the boundary line of the departure of the Palaeoblattariae toward later forms 

 (those paleozoic cockroaches allied to Petrablattina) and especially those [Palaeoblatta- 

 riae] 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 toward the base of the wing, wdiose few remaining 

 branches finally become attached to the scapular vein, no trace of their former depend- 

 ence remaining visible." 2 



The present study shows that this conclusion must also be modified b} r a somewhat 

 further extension. The above statement is true of about two-thirds of the species, but 

 there are also others, both in the Lias and the Oolite, in which a different or even a 

 greater variation is found, the externomedian vein being sometimes united, throughout 

 at least part of its length. With the scapular, or it may be wholly united with the inter- 

 nomedian, and in both cases, the mediastinal may or may not also be united with the 

 scapular. The variation is therefore already very great in Liassic times, although it 

 reached its maximum only in the later Oolite. AVith the exception then of about a 

 dozen species of Palaeoblattariae in the Triassic rocks, all of the mesozoic cockroaches, 

 like the living, have front wings in which two or more of the veins are coalesced. 



As regards the other distinction, drawn from the anal area, there is much diversity, 



■Mem. Bost. Soc. Sat. Hist, m, 38. 'Amcr. Jonrn. Sc. (3) xxvm, 201. 



