THE PREDACEOUS DIVING BEETLES. 



217 



c. Thorax strongly margined, sparsely but distinctly punctate. 



417. STAG IN A LI S. 



ee. Thorax linely margined, almost smooth. oblitus. 

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

 thorax darker than elytra. 418. vms. 



Hind coxa? contiguous. 



/. Form elongate, obconie; antenna? of male with joints 3-5 dilated; 



length 5.5-6 mm. 419. diffoemis. 



//. Form oval or oblong-oval; antenna? of male not dilated; length not 



more than 5 mm. 



g. Under surface reddish-brown; side margins of thorax generally 

 thickened. 



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

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

 yellow. 420. stkiatopunctatus. 



///;. Elytra without smooth lines. 



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

 or spots of reddish-brown. 



Thorax finely and indistinctly margined. 421. consimilis, 

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

 U. Clypeus rounded, not margined. 



k. Elytra blackish with yellow markings ; form elongate-oval ; 

 thorax not infuscate. mixtus. 

 kk. 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. sekiceus. 



II. Thorax narrowly fuscous at base; form subdepressed ; 



pubescence much less distinct. 423. dimidiatus. 



gg. Under surface (except sometimes the abdomen) black or piceous; 

 side margins of thorax not thickened, 

 m. Thorax evenly and regularly punctate. 



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



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

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

 or nearly so. 



o. 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. dichrous. 



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

 thorax ; elytra distinctly punctate; length 4 mm. 



428. AMERICANUS. 



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

 length 4 mm. tenebrosus. 



