EXPLANATION OF STEUCTUEAIj 

 PLATES. 



upper 



Fig. II. Diagram of an imaginary beetle displaying the various 

 portions of the under skeleton, some of which are always either absent 

 or obsolete. 



1 . Gular region. 



2. Collum. 



3. Prosternum. a. episternum ; h. epimeron. 



4. Mesosternum. c. episternum. d. epimeron. <: paracoxa or 

 trochantin (shown l)y a fine line drawn through it). 



5. Metasternum, /. episternum. g. epimeron. 



The paracoxa or trochantin is present in some genera, but not in 

 others : the epimera of the prosternum are always small, and often 

 incons})icuous or obsolete. 



Fig. III. Under- skeleton of Gyrinus. 



1. Prosterniim. a. episternum. h. epimeron. 



2. Mesosternum. c. episternum. d. epimeron. 



3. Metasternum. e. episternum. /. epimeron. 



On the first segment of the abdomen the rudiments of the suture of 

 another segment are more or less distinctly visible. 



Fig. IV. Dyfiscus marginalis, L. {male) : under side. 



1. Ist ventral segment of abdomen. 4. 4th ventral segment of abdomen 



2. 2nd „ ^ „ 5. 5th 



3. 3rd ,. „ G. Gill 



