THE BRITISH WOODLICE. 



39 



which has been named Avchaoniscus brodiei, and is said to be 

 referable to the recent family Aegidae is found in some numbers 

 in the Purbeck Beds (Upper Jurassic), of this country (47). 

 Fossil Isopods have also been recorded from the Oolite and 

 from the Oligocene (Isle of Wight). 



Turning to the Woodlice proper, we find that they first make 

 their appearance in the Miocene (of Oenigen and Baden), and 

 occur also in amber (79) ; while examples of the genera, such as 

 Oniscus and Porcellio, have been discovered in late Tertiary 

 deposits (47). 



External structure and appendages. — Woodlice agree 



Za&ral 



Tete 



>07V 



ABDOMEN 



FIG. I. — PARTS OF THE BCDV 



(Oniscus osellus.) 



in being of a somewhat oval form, and their bodies are arched, 

 the curve varying in different genera and species. A head is to 

 be distinguished ; behind this comes the thorax of seven segments 

 which are often considerably broader than the six succeeding 

 ones which form the abdomen (see fig. 1.) 



The head carries two large antennae (fig. 3) 

 which are very evident, and a careful search 

 with a lens will reveal a second and minute 

 pair (the smaller antennae) situated between the 

 base of the others, and really anterior to them, 

 (figs. 2 and 4.) 



The larger antennae are customarily bent 

 at certain points, and we can distinguish a 



FIG. 2.-THE FIRST 

 ANTENNA. 



(Oniscus asellus.) 



