THE YOUNG 



NATURALIST. 



213 



deep pit or depression at each side of the 

 base. The three species, P. excavatus, P. 

 assimilis, and P. septentrionis, possess a great 

 general resemblance and are not easily dis- 

 tinguished on paper. The first two species 

 are apterous, but septentrionis is furnished 

 with wings, is more parallel sided, and has 

 a shorter thorax than either of the other 

 species. Assimilis differs from excavatus in 

 the fact that the striae on the elytra com- 

 pletely disappear before the sides and apex, 

 whilst in excavatus they are present, though 

 faint. All three species measure about 

 ^-inch in length, and are generally, but not 

 always, taken in mountainous districts, 

 excavatus being the commonest and most 

 widely distributed species. 



POGONUS. 

 This genus also contains three British 

 species, viz., hmdipennis, littoralis, and 

 chalceus, all of which are moderately com- 

 mon on the muddy banks of rivers. The 

 species are very easily distinguished as 

 follows : — 



A. Head and thorax green ; elytra yellow. 

 Length 35 lines luridipennis 



B. Head, thorax, and elytra hronze. 

 Elytra broad and rounded at the sides, 



Length lines .chalceus. 



Elytra narrow and parallel sided. 

 Length 3 lines littoralis 



Family TRECHID^E. 



The British species of this family are dis- 

 tributed among three genera, Trechus, ^pus, 

 and Perileptus. These genera are easily 

 distinguished as follows : — 



A. Size over 1 line Trechus. 



B. Size I line. 



Elytra without strias Mpus 



Elytra with striae ^although these are 

 faint at sides and apex) . . Perileptus. 



TRECHUS. 

 This genus contains nine British species, 

 several of which are rare. They are not 

 easily distinguished from one another ex- 



cept by comparison side by side, but the 

 following arrangement will, to a certain 

 extent, be serviceable to a beginner : — 



A. Elytra oUong, with parallel sides. 



1. Elytra red, with a distinct bluish 

 black band across the hinder portion, 

 Length 2.\ lines discus, 



2. Elytra red, with a faint darker mark- 

 ing behind the middle ; strise near 

 the suture very fine ; length 2 lines. . 



micros. 



3. Elytra brownish without dark spots; 

 striae near the suture deep ; length, 

 if lines longicornis, 



B. Elytra ovate; with the sides more or less 



rounded. 



a. Posterior angles of the thorax more or 

 less distinct, even if odtuse. 



Length over 2 lines. 



4. Thorax yellowish ; elytra flat 



lapidosus. 



5. Thorax brown; elytra convex 



rubens. 



Length not over 2 lines. 



6. Elytra with the four striae nearest 

 the suture equally distinct ; posterior 

 angles of the thorax fairly distinct, 

 and the sides not much rounded. 

 Length, I5 lines minutus. 



7. Elytra with only the two striae next 

 the suture at all distinct ; posterior 

 angles of the thorax not so distinct, 

 sides of thorax more rounded, and the 

 elytra shorter ; length, 1 1 lines-obtusus. 



8. Elytra with three deep furrows on 

 each side of the suture ; posterior 

 angles of the thorax right angles ; 

 length, 2 lines rivularis. 



b. Posterior angles of the thorax com- 

 pletely rounded seoalis. 



Of the above species, only one [minutus) is 

 at all abundant, and this occurs everywhere 

 under stones, at tree roots, &c. Discus, 

 rubens, oMusus, and secalis, are fairly com- 

 mon, principally haunting the dry banks of 

 streams, running off and hiding themselves 



