244 COLEOPTERA CHAP. 



Although the characters of these Insects are not very different 

 from those of Byrrhidae, of Dascillidae, and even of certain 

 Elateridae, there is practically but little difficulty in distinguish- 

 ing Parnidae. They are of aquatic habits, though many, in the 

 perfect state, frequently desert the waters. There are about 

 300 or 400 species known, but the family is doubtless more 

 extensive, as these small beetles attract but little notice. There 

 are two groups: 1. Parnides, in which the front coxae have a con- 

 siderable transverse extension, the antennae are frequently short 

 and of peculiar structure, and the body is usually clothed with 

 a peculiar, dense pubescence. 2. Elmides, with round front coxae, 

 a bare, or feebly pubescent body, and simple antennae. Parnus 

 is a genus commonly met with in "Europe, and is less aquatic in 

 habits than its congeners ; it is said to enter the water carrying 

 with it a coating of air attached to its pubescence. Its larvae 

 are not well known; they live in damp earth near streams, and 

 are said to much resemble the larvae of Elateridae. Potamophilus 

 acuminatus has a very interesting larva, described by Dufour ; it 

 lives on decaying wood in the Adour. It is remarkable from 

 the ocelli being arranged so as to form an almost true eye on 

 each side of the head ; there are eight pairs of abdominal 

 spiracles, and also a pair on the mesothorax, though there are 

 none on the pro- or meta-thorax ; each of the stigmata has four 

 elongate sacs between it and the main tracheal tube ; the body 

 is terminated by a process from which there can be protruded 

 bunches of filamentous branchiae. The larvae of Macrony/i //-s 

 quadrituberculatus is somewhat similar, though the features of its 

 external structure are less remarkable. The Elmides live attached 

 to stones in streams ; the larva is rather broad, fringed at the 

 sides of the body, and bears behind three elegant sets of fine 

 filamentous branchiae. The North American genus Psephenus 

 is placed in Parnidae, though instead of five, the male has 

 seven, the female six, visible ventral segments ; the larva is 

 elliptical, with dilated margins to the body. Friederich, has 

 given, 1 without mentioning any names, a detailed account 

 of Brazilian Parnid larvae, that may perhaps be allied to 

 Psephenus. 



Fam. 49. Derodontidae. Tarsi Jive-jointed, slender, fourth 

 joint rather small; front coxae prominent and transversely pro- 

 1 Stettin, ent. Zeit. xlii. 1881, pp. 104-112. 



