164 COLEOPTERA OF NORTH AMERICA. 



broadly emargiimte, the sixth deeply bilobed, only visible around 

 the emargination of the fifth, seventh rounded, entire, filling the 

 emargination of the sixth ; in the 9 the sixth ventral segment of 

 the I disappears. The body is clothed with the same fine pubes- 

 cence that characterizes the other sub-families, enabling a film of 

 air to be preserved beneath the water. 



One genus Psephenus Lee. represents this sub-family. Two 

 species are known P. Leconiei Ilald. from the Atlantic region 

 and P. Maldemani Horn from Lower California. 



The larva is an elliptical ol)ject, with the margins widely ex- 

 tended beyond the body, and is seen on stones under the water of 

 rapid streams; it is especially abundant in the rapids of Niagara, 

 and differs in no important particular from the larva of Helichus, 

 of the next sub-family. It respires by branchial filaments. 



Sub-Family II._PARNIN^E. 



The anterior coxie are transverse, with a distinct trochantin; 

 the posterior coxa3 dilated into a plate; the abdomen has five 

 ventral segments, the fifth rounded at the tip; the front is not 

 ])rominent, as in Psephenidse, and the oral organs are anterior; 

 the palpi are short. The other characters are still variable, and 

 will furnish occasion for the division into tribes. 



Head not entirely retractile ; prosternum not lobed in front ; antennae 

 elongate, serrate, with the first and second joints not enlarged. Larini. 



Head retractile, protected by a prosternal lobe ; antennte short, first and 

 second joints enlarged. Parnini. 



Trit)e I.— LARINI. 



The only representative known to us is Lara avara Lee, from 

 Oaiifornia, an elongate, blackish insect, finely pubescent, with the 

 elytra punctured in rows, impressed behind the base, and the 

 thorax strongly narrowed in front, somewhat uneven; the antenna) 

 are long and slender, distant from each other, and feebly sub- 

 serrate, and not irregular or short; the clypeal suture is distinct; 

 tfie head is not protected beneath by a lobe of the prosternum ; 

 the anterior coxfe are somewhat prominent, the trochantin large, 

 free, and very distinct; tiie prosternal process is narrow; the 

 nu'sosternum is prominent, deeply excavated ; the middle coxai 

 aro widely separated, and have distinct trochantin; the side ])ieces 



