COLEOPTERA. 



41 



we have no fixed system of classification or method of arranging 

 beetles. In catalogues they are generally grouped into families 

 according to the number of joints of the tarsi : thus those " possessing 

 five joints to all the tarsi have been termed Pentamera ; those with 

 five joints to the front and middle legs, and only four to the hinder, 

 //' teromera ; those with apparently only four to all the tarsi, Tetramera; 

 and those with apparently only three to all the tarsi, Trimera." 1 



In looking over a list of Coleoptera, the systematic student will 

 obviously note that he enters the domain of beetles associated with 

 forest trees deep down in his list. It is also, however, somewhat 



Fig. 42 Typical beetle : Dytiscus marginalis, 



/.. (male), under side (water-beetle). (From 

 Fowler's ' British Coleoptera.') 



1. 1st ventral segment of abdomen. 



2 9nd 



o. orcl ,, ,, ,, 



4. 4th 



5. 5th ,, 



6. 6th ,, ,, 



7. Presternum, terminating in prosternal 



process. 

 S. Episternum of prosternnm. 

 9. Episternum of mesosternum. 



10. Epimeron of mesosternum. 



11. Metasternum. 



12. Wing of metasternum. 



13. Episternum of metasternum. 



14. Coxal cavities. 



15. Cox* (posterior pair very largely devel- 



oped for the support of the swimming 

 legs). 



16. Trochanter. 



17. Femur. 



18. Tibia. 



19. Dilated tarsus or palette, and cupules 



of male. 



20. Oar-shaped tarsus. 



21. Coxal process. 



22. Epipleura of elytra. 



23. Genital armature. 



remarkable, so far as hunting-ground is concerned, that where the 

 student in forest insects begins, the systematic man and the student 

 of many forest insects might claim mutual association all along a 

 considerable portion of the list. It is, however, only essential to 

 select the more salient species, and in doing so many arboreal species 

 will have to be omitted. On the other hand, so as to present any- 

 thing like completeness, many species would have to be considered 

 which are not of great importance from the purely economic point 

 of view. 



As regards the details of structure, the student would do well to 

 refer to figs. 41 and 42, together with the explanation as given by 



1 Rye, British Beetles, p. 41. 



