COLEOPTERA OF NORTH AMERICA. 



Fam. vl— GYRINIDAE. 



Mentum deeply emarginate; lateral lobes rounded; gular 

 suture distinct. 



Ligula lai-ge, quadrate, corneous, filling the emargination 

 of the mentuni, palpi o-jointed. 



Maxillae with the outer lobe usually wanting, sometimes 

 slender, not articulated, the inner one curved, ciliate inter- 

 nally, acute at tip ; palpi 4:-jointed, last joint as long as the 

 others united. 



Eyes divided by the sides of the head, upper and lower 

 parts both rounded. 



Antennae inserted under the sides of the front, behind the 

 base of the mandibles, short, thick, third joint auriculate, 

 subsequent ones transverse, last joint elongate. 



Prothorax with the prosternum short and carinated, epi- 

 sterna and epimera distinct, the latter large. 



Mesosternum very large, rhomboidal, posterior angle 

 emarginate for the reception of the point of metasternum; 

 episterna and epimera entirely connate, attaining the middle 

 coxae. 



Metasternum very short, pointed before and behind, with- 

 out ante-coxal piece; episterna very large; epimera not 

 visible. 



Coxa?, anterior, small, globular; middle, flat, oblique, 

 almost reaching to the posterior coxae behind; the latter 

 are large, truncate anteriorly, contiguous, at their inner 

 margin, extending to the margin of the body, and thus sepa- 

 rating entirely tlie ventral segments from the metasternum; 

 they are dilated internally, and broadly excavated behind 

 for the motion of the hind legs. 



Abdomen 7-jointed, the three anterior segments connate, 

 the first suture almost obsolete; the seventh longer than 

 the sixth, rounded at tip. 



Anterior legs very long, received in oblique grooves of 

 the pro- and mesosternal segments; tibire slender, with one 

 terminal spur; tarsi o-jointed, of the male sometimes dilated. 



Middle and posterior legs short, broad, very much com- 

 pressed; tibio? without spurs; tarsi 5-jointed ; first joint of 

 middle feet large, triangular; second and third very short; 

 fourth large, triangular; fifth triangular, with two approxi- 

 mate claws. Of the posterior feet of Dineutus the first joint 

 is very large; the others are small, and diminish gradually 

 in size, the last with two ver^'- small claws. In Gyrinus the 

 posterior and middle tarsi ai'c nearly alike. 



