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IV. — Synthesis, or Classification. 

 F I E S T SYNTHESIS (G E N E II A). 



I. 1.— Genus PELOBIUS. {Vide p. 259.) 



This aggregate is formed by three species ; their individuals are of moderate size 

 (about 10 m.m. in length), the form is short and broad, very convex beneath, the 

 surface very densely punctured, without pubescence. 



The head is exserted from, and little clasped by the angles of the thorax ; the 

 eyes are convex, prominent, and not touched by the thoracic angles; the labrum is 

 quite exposed in front of the clypeus, and perfectly continuous in plane with it ; the 

 suture separating the clypeus, or epistoma, from the forehead, is angulated in the 

 middle (and is very distinct in the Eui-opean, nearly obliterated in the Austrahan 

 species) ; the buccal and gular sutures are fine but distinct in Dytiscus tardus, nearly 

 obliterated in Pelobius niger ; the antenna is inserted in a small cavity situated at 

 the upper part of a rather large, subtriangular glabrous space, and is 11-jointed; the 

 basal joint is much larger than any of the others and more or less punctate, the 

 other joints are without punctuation, but each bears on the ujsper surface quite at 

 the extremity, a minute round cavity ; none of the joints has any pubescence, or 

 elongate setae ; but by very minute examination it can be seen that there are, at any 

 rate on the three or four basal joints, the rudiments of a few setae. 



The mentum is very short, its lateral lobes extremely short ; the palpi are rather 

 short and stout ; the outer lobe of the maxilla is rather obscurely biarticulate. 



The prothorax has the sides of the upper surface distinctly, and the anterior 

 margins both of the pronotum and prosternum densely ciliate ; the prosternum along 

 the middle, assumes directly at the front margin a vertical direction, and shortly 

 thereafter is turned backwards and continued so as to form a thick, prominent, 

 prosternal process; this process is not broad but is elongate, and is nearly acuminate 

 at the apex, it is margined at the sides, and the margins are continued forwards 

 between the front legs, till they attain the anterior vertical portion of the prosternum; 

 the prosternal sutures are indistinct as are also those of the side pieces; the form 

 of the prothorax is such as to give it a great extension in the vertical direction ; thus 

 the depth from the hind margin of the pronotum to the apex of the prosternal process 

 ]ii 4 m.m., this measurement being distinctly greater than the width of the prosternum ; 

 this considerable depth enables the front coxse to be conical and elongate; their 

 cavities are closed behind by a large corneous process, connecting the inner faces of 

 the two epimera. 



TRANS. EOT. DUB. SOC, N.S., VOL n. SO 



