COLEOPTERA. 525 



The best way to obtain specimens is to sweep the vege- 

 tation growing on the bottom of a quiet pool with a dip- 

 net. 



The larger of our common species belong to Cybister 

 (Cy-bis'ter), Dytiscus (Dy-tis'cus), and al- 

 lied genera. In Cybister the little cups 

 on the under side of the tarsal disks of 

 the male are similar, and arranged in four 

 rows. In Dytiscus and its allies the cups 

 of the tarsal disks vary in size. Figure 

 633 represents a common species of Dy- 

 tiscus. Fig. 633. 



The most common of the diving-beetles that are of 

 medium size belong to the genus Acilius (A-cil'i-us). In 

 this genus the elytra are densely punctured with very fine 

 punctures, and the females usually have four furrows in 

 each wing-cover (Fig. 631). 



There are also common diving-beetles that are of about 

 the same size as the preceding, but which have the wing- 

 covers marked with numerous very fine transverse striae ; 

 these belong to the genus Co/ymbetes (Col-ym-be'tes). 



Of the smaller diving-beetles, measuring less than one 

 fourth of an inch in length, many species can be found in 

 almost any pond. These represent many genera. 



Family GyrixiD/E (Gy-rin'i-dae). 



The Whirligig-beetles. 



As familiar to the country rover as the gurgling of the 

 brook, or the flecks of foam on its " golden-braided centre," 

 or the trailing ferns and the rustling rushes on its banks, 

 are these whirligigs on its pools. Around and around each 

 other they dart, tracing graceful curves on the water, which 

 vanish almost as soon as made. They are social fellows, 

 and are almost always found in large numbers, either swim- 

 ming or resting motionless near together. They rarely dive, 

 except when pursued ; but are so agile that it is extremely 



