On Aquatic Carnivorous Colcoptera or DytiscidcB. 395 



wing-cases. They may be arranged in three groups as follows ; (but the distinction 

 between the groups is not very marked, many of the species of the third group 

 approximating to the preceding ones by the labrum being more or less retracted, 

 and the front of the head not very distinctly emarginate). 



Group. 1. — Labrum much concealed, head rounded in front, and with a more or 

 less distinct raised margin : form usually very short, (the margin on 

 the head is always fine, sometimes very indistinct and obsolete). 

 Species 381 to 3S9. 



Group. 2. — Head rounded in front, and with a thick, but little elevated margin j 

 labrum moderately concealed, approaching so nearly to the upper- 

 surface of the head, that there is a slight interruption in the middle 

 of the thickened margin. Form short or rather short. Species 390 

 to 392. 



Group. 3. — Front of head without margin, and truncate-emarsfinate in the middle 

 in front, labrum little concealed or quite conspicuous ; form oval, 

 more or less elongate. Species 393 to 423. 



Group 1. 



381. Dytiscus insequaJis, Fab., Hydroporus incequalis, M.C. — Brevis, convexus, 

 sat latus, nitidus, sine pubescentia, ferruginous, prothorace basi apiceque nigro, 

 elytris nigris margine externo signaturisque ferrugineis ; capite thoraceque crebre 

 subtiliter, elytris crebre fortiter punctatis ; pectore fortiter, abdomine sat fortiter 

 punctatis. Long. 3, lat. 2 m.m. 



The markings on the elytra are variable, the sutural portion is always black and 

 the external portion yellowish ; sometimes the black portion is broken by some 

 yellow irregular marks. 



A variety nearly black in colour from Armenia is in the collection of Wehncke. 



Abundant in Northern and Middle Europe ; (Algeria, Wehncke). According to Crotch the species 

 has also been found in Illinois, North America. 1 7.5. 



382. Hydroporus punctatus. Say, M.C. — Brevis, convexus, latus, sine pubes- 

 centia, ferrugineus, prothorace basi elytrisque obscurioribus, his margine externo 

 dilutiore, capite thoraceque crebre punctatis ; elytris crebre fortiter punctatis ; 

 pectore fortiter, abdomine sat fortiter punctatis. Long. 3, lat. 2 m.m. 



Closely allied to Dytiscus ina^qualis, (No. 381), but rather different in outline, 

 being broader in the middle and so less parallel in form, with the punctuation of 

 the elytra I'ather dense, and the upper surface without distinct contrasts of colour. 



United States of North America, (Middle and Western States). 17G. 



TRANS. BOY. DL'B. SOC, N.S., VOL. II. 3 F 



