with Descriptions of New Forms. 117 



little by supplying important types from the National Museum 

 collection. The specimens sent by Mr. Daniels have been of 

 the greatest interest, as adding to the collections from the 

 famous Mazon Creek locality. 



Nomenclature used in dealing with the Nymphs. — In attempt- 

 ing the study of a collection of fossil cockroaches, including 

 numerous specimens in the nymph stages, the investigator is 

 met at the outset by the perplexing question of nomenclature. 

 It will rarely be found possible to identify all the nymphs with 

 their respective adult species. When only a few nymphs are 

 to be dealt with, no great inconvenience results from simply 

 referring them to their tribe, or genus, if possible, as immature 

 forms. But when, as in the present instance, a large number 

 are at hand which separate themselves naturally into specific 

 groups, some means of designating a group as a whole becomes 

 practically necessary. Accordingly, in a few instances specific 

 names have been retained or proposed for well-defined species 

 as a means of reference until their connection with adults 

 can be established. Inasmuch as it is difficult, if not impos- 

 sible, to distinguish the closely related genera of the tribe 

 Mylacridse in the nymph condition, it has been thought admis- 

 sible to use the type genus Mylacris in a somewhat extended 

 sense, to include the nymphs of the tribe. Etoblattina is used 

 in the same way to some extent for the Blattinariae, although 

 this tribe is more varied, and generic characters seem to appear 

 earlier. 



Terminology of the Veins of the Wing. — The system of 

 designating the veins used in the description of species in the 

 present paper is that developed by Redtenbacher and now for- 

 tunately coming into general use in entomology. This recog- 

 nizes in the typical wing five main veins, aside from those of 

 the anal area. It is much to the credit of this system that it 

 is readily applicable to the wings of the simple and compara- 

 tively unspecialized insects of the paleozoic. A great deal has 

 been done in recent years to establish the essential unity of the 

 plan of structure of the wing and to discover the homologies 

 of the main veins in the different orders of insects, with the 

 result that many entomologists are now convinced that all 

 winged insects have descended from a common winged ancestor. 

 The complicated arrangement of the veins, so difficult to 

 decij^her in the wings of many living adult insects, becomes 

 more and more simple as the phylum is traced toward its point 

 of origin. As paleontological evidence becomes more complete, 

 the steps in the differentiation of the wing can be more closely 

 followed. Inasmuch as the terminology of the veins and their 



