THE GROUND BEETLES. 157 



scutellum distinct. Elytra not margined at base, apex truncate 

 and with a membranous border: disk not or very feebly striate 

 and without dorsal punctures. Prosternum not prolonged. Tarsi 

 slender, the front pair in the males with three joints feebly di- 

 lated and covered with small scales beneath. The only genus in the 

 United States fauna is 



LIV. BRACHYNUS Wei). 1801. (Gr., "short + back.") 



Small or medium sized beetles with broad abdomen and narrow 

 head and thorax. The elytra are of a dark blue, blackish- or 

 greenish-blue color, while the head, thorax and legs are reddish- 

 yellow. The generic name refers to the shortness of the elytra. 



They occur under logs or stones, usually in damp 

 places. In early spring some of the species are es- 

 pecially abundant and often gregarious in small 

 colonies. When disturbed they emit from a little 

 internal sac near the end of the abdomen a pun- 

 gent, volatile fluid which serves them as a means 

 of defense. This fluid is ejected with a sound like 

 that of a small popgun, and when it comes in con- 

 tact with the air it changes to a gas which appears Fig.se. Brachynus sty- 

 like steam. For this reason the members of the 

 genus are known as "bombardier beetles." When pursued by 

 some larger insect the bombardier discharges a part of the stored 

 liquid into the face of its enemy, the noise and gas so disconcert- 

 ing the pursuer that the bombardier often has time to escape. 

 Some forms are capable of discharging four or five times in suc- 

 cession. 



But one paper has been issued on the United States species of 

 the genus, viz. : 



LeCoutc. "Notes on the species of Brachiuus inhabiting the 

 United States," in Proc. Phil. Acad. Nat. Sci., 1862, 523. 



This does not include all of the North American species now 

 known, about 26 in number. The distinguishing characters are so 

 few that no satisfactory table is extant. Sixteen different forms 

 have been taken in Indiana. These were submitted to Mr. Liebeck, 

 who wrote me concerning them as follows: 



"I assorted your lot of Brachynus and determined them by 

 comparison with the species in the Horn collection, which is Hie 

 best I could do. There the species are arranged in the order in 

 which they are listed by Henshaw, which differs from the old Le- 



