THE PREDACEOUS DIVING BEETLES. 217 



'■. I'lun-iix sU-ciiigly iiiiir.^iuod. sparsely but (listhiiUy punflalo. 



417, STAGNAI.IK. 



te. Thorax finely margined, almost smooth. oblitis. 



''f'. Under surface reddish-brown ; prosternal process small ; head and 

 thorax darker than elytra. 418. vilis. 



. Hind coxaj contisnons. 

 /. Form elongate, obconic; antennae of male with .ioints 3-5 dilated; 

 length 5.5-(i mm. 419. difformis. 



//. Form oval or oblong-oAal ; antennae of male not dilated; length not 

 more than 5 mm. 

 g. Under surface redrtish-bro^n ; side margins of thorax generally 

 thickened. 

 h. Elytra coarsely punctured, with two smooth, narrow lines on 

 each; above black or picenus, head and elytral markings dull 

 yellow. 420. stkiatopunctatus. 



hli. Elytra without smooth lines. 



i. Clypeus rounded, broadly margined ; elytra blackish with bars 

 or spots of reddish-brown. 

 j. Thorax finely and indistinctly margined. 421. consimilis. 

 jj. Thorax broadly and distinctly margined. 422. rNnuiATis. 

 a. Clypeus rounded, not margined. 



7i. Elytra blackish with yellow markings ; form elongate-oval ; 

 thorax not infuscate. mixtus. 



7i/i'. Elytra reddish-yellow with elongate or oblong black mark- 

 ings. 

 I. Thorax with base and apex fuscous; form convex; sur- 

 face with dense fine yellow pubescence. seeicetjs. 

 II. Thorax narrowly fuscous at base ; form subdepressed ; 

 pubescence much less distinct. 423. dimidiatus. 

 gg. Under surface (except sometimes the abdomen) b^ack or piceous ; 

 side margins of thorax not thickened. 

 m. Thorax evenly and regularly punctate. 



n. Punctures of elytra distinct ; length 4 mm. 424. nigek. 



nn. Punctures of elytra indistinct ; length 5 mm. 425. modestus. 

 mm. Thorax unevenly and irregularly punctate, the disk often smooth, 

 or nearly so. 

 0. Thorax finely and somewhat indistinctly margined at the sides, 

 p. Abdomen reddish-brown, paler than meso- and metathorax ; 

 elytra finely and indistinctly punctured. 

 q. Elytra piceous ; form more slender and parallel ; length 

 3-3.5 mm. 426. pboximus. 



qq. Elytra reddish-brown ; form broader in front, more pointed 

 behind ; length 4 mm. 427. dichbous. 



pp. Abdomen black or piceous, not paler tlian meso- and meta- 

 thorax ; elytra distinctly punctate ; length 4 mm. 



428. AMEBICANUS. 



00. Thorax distinctly margined at sides ; black, legs reddish-brown ; 

 length 4 mm. tenebbosus. 



