Tin; win imick; KKi'rri.i'S. 2^7 



(Misly at any small iiiscd llicy iiicd ii|>(i!i the surlai-c ol' the watcf. 

 S(>iii''t iiiics llic oiilsidfi- hccoiiics alai'iiiiMl and skalcs hack at t'lill 

 speed into the assenihly. [)uflinii' its nieinhers into wild stampede. 



Althoupli easily roeogni/.ed by tluMV t'oi-ni and hal)its. the Oifrl- 

 iiidd ai'e distingllislied ri'oiii allied faiuilie-; Ity liaxiiiL;' the e\-es 

 (•oni|iletely dividend l)y the sides of tlio head into 

 iip|)ei- and lowei- parts. l)oth rounded, so thai 

 tlie\ appear to lia\'e t'onr eyes, two For looking' 

 np into the air and Iwd Tor iiazinu' down into the 

 water. [h''\i2:. ll'O. i 'IMie antenna' are very 

 slioi'l. thick. insei-te(| Ix'hind the inandihles, tlic 

 third joint enlarged so as to resemble an ex- 

 tei-nal ear, the followiiii-' joints rather broad and biafe.^w^^Ltl-'^o silow'd^^ 

 united so as to form a si)indle-sliaped append- ''"''"' ''^''- ^'^f^'*^-- ^''''^"■"•) 

 i\g;e (Fio-. 4, No. !()) ; front legs very long, rather slender, and when 

 at rest i)laeed in oblique grooves between the pro- and mesostema; 

 middle and hind legs short, broad, \ery much flattened; tibiae with- 

 out spurs; tarsi 5-jointed. the joints in part flattened and trian- 

 gular. 



The eggs of the Gyrinid;i? are laid in parallel rows upon the 

 leaves of aquatic plants. The grubs are long, narrow and much 

 flattened, aiui breathe by means of tracheal gills attached to the 

 abdominal segments. (Fig. 121.) They are chiefly carnivorous, 

 and when full grown leave the water and spin a gray, paper-like co- 

 coon on some nearby object, in which they undergo the pupal stage. 



Only about 40 species of Gyrinida' are known from the United 

 States. These are divided among three genera, two of which are 

 known to occur in the State, while the single species of the third 

 is recorded from Quincy, Illinois, and may yet be found in the 

 western part of Indiana. 



The only papers treating of the North American species of the 

 family are as follows : 



LeConte. — "The Gyrinicte of America North of Mexico," in 



Proc. Phil. Acad. Nat. Sci., 1868. 865. 

 Rohprts, C. H. — "The Species of Dineutes of America North of 



Mexico," in Trans. Amer. Ent. Soc, XXII, 1895, 279. 



KEY TO CENEKA OE (;YRINn).T:. 



ft. Last ventral segment depressed, munded at ti'it. 



Ii. Scntellnm distinct; lenjjtli Ics.s tlian 8 mm. I. Gyrinus. 



1)1). Scutolinm invisii)le; iabrum transverse; lengtli '.i ei' iimre mni. 



II. Dineutes. 



