8 CLAVICORNIA. 



legs of wliicli the til)ia3 are compressed and generally sulcate for the recep- 

 tion of the tarsi, and also by the connate anterior segments of the 

 abdomen, as well as by the usually striated elytra ; the antennae are, as a 

 rule, 11-jointed, rarely 10 jointed, with the apical joints, in our genera, 

 forming a club ; the anterior coxal cavities are open behind ; the elytra 

 cover the abdomen, which is composed of five segments, of which the 

 first two or three are usually connate ; the tarsi are 5-jointed, Avith the 

 hist joint elongate, except iwAspidiphorus, in which they are heteromerous; 

 the species are short, oval, and very convex, and vary very much in size. 



G-eoryssidae. This and the succeeding family are more or less 

 aquatic in their habits, and by some authors are placed near the Hydro- 

 philidae ; the family Georyssida^ contains a single genus, Georyssus, 

 which is very closely allied to Elmis, but may at once be distinguished 

 by the distinct 3-jointed club of the antennse, and the short 4-jointed 

 tarsi ; all the coxae are distant, and the anterior pair are compressed and 

 flattened at the tip, forming two plates which conceal the prosternum ; 

 according to Thomson these plates are formed by the laminate tro- 

 chanters ; the elytra are entire, and are very roughly sculi)tured ; the 

 abdomen is composed of five segments, of which the first is very large and 

 the last three are free. 



Parnidae. The following are the chief characteristics of this family, 

 which has by many authors been divided into two separate families, 

 the Parnidae and Elmidce : head usually retractile ; antennae variable, 

 either filiform and moderately long, as in Elmis, or very short, with the 

 second joint dilated and ear-shaped, as in Parnus ; eyes rounded, some- 

 times hairy : anterior coxal cavities open behind, all the coxse distant ; 

 prosternum prolonged behind the coxa3 ; legs slender, sometimes very 

 long, tarsi 5-jointed, with joints 1-4 short, equal, fifth very long, claws 

 strong, simple ; abdomen in our genera composed of five ventral segments ; 

 upper surface strongly pubescent, and often pilose, in the Parnina,and 

 the form larger and sul)cylindrical ; in the Elmina the pubescence is 

 very fine and scanty, and the form is more depressed and much smaller. 



Xleteroceridae. An aberrant family, of somewhat doubtful affinities, 

 containing a single genus Heterocerus, which by its subaquatic habits, 

 general form, strong pubescence, and very short antennee, appears to be 

 allied to Parnus, but differs in several very important points; the 

 following are its chief characters ; head large, with the eyes half-hidden, 

 antennse short, inserted above the base of the mandibles near the inner 

 margin of the eyes, with first two joints large and ciliate, and joints 

 5-11 forming an oblong serrate club; thorax transverse with the angles 

 rounded, and the anterior coxal cavities open behind ; elytra completely 

 covering abdomen, which is composed of five ventral segments, of which 

 the two last are free, and the first is furnished with a stridulating org:in ; 

 legs fossorial, tarsi 5-jointed, apparently 4-jointed, the first joint being 

 minute and obsolete; size 2\-5\ mm. 



