30S Sellards — Structural Characters of Cockroaches. 



from the ( loal Measures. The paper is now nearing completion, 

 but as some time will necessarily elapse before its publication, 

 it seems best to give in advance the results of more immediate 

 interest. 



The material on which this study is based is mostly of Coal 

 Measure age, and is contained in the collections of the Yale 

 University Museum, the University of Kansas Museum, the 

 National Museum, and in the private collection of the writer. 

 The principal localities represented are Mazon Creek, Illinois, 

 and Lawrence, Kansas. 



From the favorable preservation of the fossils contained in 

 these large collections, it has been possible to give a more com- 

 plete account of the structure of Paleozoic cockroaches than 

 has been given heretofore. Additions have been made to a 

 knowledge of the structure of the head, antennae, eyes, legs, 

 hind wings, dorsal and ventral sides of the abdomen, oviposi- 

 tors, and cerci. The larval stages of several species have also 

 been discovered. 



The head is more or less completely preserved on a number 

 of specimens. Occasionally the eyes and antennae, which have 

 not been previously observed, are present. The cerci vary a 

 good deal in length in the different genera and species, and are 

 directed either obliquely or at right angles to the body. 



Nymphs. — An unusual feature of these collections is the 

 comparative abundance of cockroaches in the immature or 

 nymph stages, or, rather, in most cases the sheddings or moults 

 of nymphs. That these fossils represent nymphs and *iot 

 wingless adults is evident not only from the presence of the 

 same species in different stages of development, but also from 

 the fact that a number of them are referable to their adult 

 genera and species, while most of them have an open slit down 

 the thorax, indicating that the part preserved is the cast-off 

 integument. These moults are particularly well adapted for 

 preservation, as on the one hand they are free from the inju- 

 rious effects of the organic juices of the body, and on the other 

 escape the danger of being eaten by other animals. The chitin 

 is hard and resistant, and yet the moults are light and like 

 the detached wings are readily carried by currents. 



The presence of nymphs at localities where the wings only 

 of adults are found, or where the bodies are but rarely pre- 

 served, is probably to be accounted for in this way. It is 

 extremely rare to find any part of the body of an adult insect, 

 other than the wings, in the Lawrence Shales. Nymphs, on 

 the contrary, as well as detached wings, are comparatively 

 numerous. The Mazon Creek nodules contain not only the 

 moults, but occasionally the bodies as well. Not a few of the 

 nymphs can be identified with their proper genera and species. 



