244 HYDROPHILID/E. \ Odlichius. 



of a straight line with a semicolon, more or less distinct on each side of 

 it(c|5). 



The transformations of Octhebius are described by M. Mathan, Ann. 

 Fr. 1865, p. 201. 



About half the European species of Octhebius are found in Britain ; 

 three of these, 0. margijmllens, 0. exaratus, and 0. Poiueri, are very- 

 minute, not, or scarcely exceeding 1 mm. in length ; one, 0. loundatus, 

 is considerably larger, reaching 3 mm. ; the remainder vary from 1|- 

 2 mm. : in determinmg the species the character of size will be found of 

 great service. 



I. Upper surface glabrous ; length not exceeding 



13 mm. ; elytra punctured in rows, 

 i. 'liiorax with a more or less distinct central 

 furiinv with transverse impressions above and 

 below. 



1. Transverse impressions of thorax continued to 



sides; length 1mm O. exaeatus, IIuls. 



2. Transverse impressions of thorax not con- 



tinued to sides. 

 A. Length 1-li mm. ; elytra bronze . . . O. marqipallens, Latr. 

 E. Length is mm.; elytra more or less 



castaneous 0. marinus, Fayk. 



ii. Tborax with well-marked central furrow, but no 

 impressions on disc. ' 



1. Head almost smooth ; punctuation weak ; 



colour golden-brassy O. ^NEUS, Ste]jh. 



2. Head rugosely punctured; punctuation strong; 



colour dark brassy O. pyom.eus, F. 



iii. Thorax with central furrow and two well- 

 marked impressions (forming a more or less dis- 

 tinct semicolon) on each side. 

 .1. Length 1| mm. ; legs red or reddish -yellow. 



A. Punctuation of elytra strong ; striaj 



distinct. 

 a. Thorax uuicolorous ; elytra longer . . O. bicolon, Germ, 

 h. Thorax with margins broadly red ; elytra 



shorter and more ovate O. RUFiMARGlNATtrs, Steph. 



B. Punctuation of elytra fine ; stria; hardly 



visible O. nanps, Steph. {aratus, 



Stepli.). 

 2. Length 1 mm. ; legs dark O. Poweri, Eye. 



II. Upper surface strongly pubescent; length 3 mm. ; 



elytra confusedly jjuuctured 0. punctatus, Steph. 



O. exaratus, Muls. Brown-black, shining, elytra sometimes rather 

 lighter ; head large, thorax transverse with a deep central furrow and 

 two transverse furrows reaching sides which at once distinguish it from 

 all the other species ; posterior angles broadly excised and filled -with 

 membrane ; elytra short oval, convex, 'with ten rows of strong, almost 

 square punctures on each, which become feebler behind ; legs red. 

 L. 1 mm. 



Very local and as a rule rare : it has, however, been found in abundance by 

 Dr. Power (who introduced it as Britisb), and also by Mr. Champion. Gravesend ; 

 Whitstable; Southend; Rainham; Lewes : it occurs in brackish ditches. 



