On Aquatic Carnworous Coleoptera or Dytiscide. 607 
resembles the male in sculpture : it has no cilize on the outer edge of the hind tarsi 
beneath, whereas in the male, both sides of the tarsi are ciliate. 
North America, (Hudson’s Bay). 1165. 
I, 62.—Genus RHANTUS. 
Side piece of fourth and following ventral segments very narrow ; metasternal 
groove distinct and well defined ; terminal joint of hind tarsus not longer, (or but 
little longer) than the preceding one ; thorax nearly always margined ; colour of 
wing-cases frequently yellow speckled with black. 
This genus as known to me comprises about forty species* ; there are but few 
parts of the world where it is not represented by one or more species. They are 
difficult to determine, and I cannot at present arrange them in natural groups that 
would make the task more easy. 
920. Colymbetes pacificus, Boisd., M.C.—Ovalis, minus convexus et elongatus, 
nigricans, vix nitidus, sublavigatus, subtilissime punctulatus, nullo modo reticula- 
tus, nigricans, vertice rufo-bimaculato, prothoracis lateribus rufis, elytris nigro 
rufoque vermiculatis, punctis seriatis magnis; antennis pedibusque rufis, pedibus 
posterioribus picescentibus; prosterno in medio minus incrassato, processu brevi, sat 
compresso; unguiculis posterioribus longitudine parum dissimilibus. Long. 94, lat. 
5 m.m. 
The male characters are very slight, the basal joints of the front and middle 
tarsi being a little incrassate, and furnished beneath with four series of extremely 
rudimentary palettes. The claws are rather short, simple, and equal. 
This very interesting species has the outer claw of the hind foot just visibly 
* The following names should probably also be assigned to the genus :—Colymbetes assimilis, Kirb, 
(No. 1,213); North America.—Colymbetes darwinii, Bab. (No. 1,219), near No. 926 ; Patagonia..— 
Colymbetes discicollis, Aubé (No. 1,221)?=No. 924; Java.—Colymbetes distigma, Brullé (No. 1,223), 
gen. dub.; South America.—Colymbetes duponti, Aubé (No. 1,225), near No. 926; South America.— 
Colymbetes fonticola, Phil. (No. 1,226); near No. 926 ; Chili—Colymbetes gutticollis, Say. (No. 1,230) 
1No. 935 Var. ; Mexico.—Colymbetes interclusus, Walk. (No. 1,234) ; Ceylon.—Colymbetes marmoratus, 
Perroud, (No. 1,239), gen. dub.; New Caledonia.—Colymbetes obscuricollis, Aube (No. 1,241) 
Qear No. 926; Chilii—Colymbetes socialis, Wat. (No. 1,250) ; Rodriguez Island.—Colymbetes suturalis, 
Macl. (No. 1,254)!=No. 1,221; Java.—Colymbetes vibicicollis, Hoch. (No. 1,257) ’=No. 924; Caucasus.— 
Hydaticus riehli, Wehncke (No. 1,320) ; Cuba.—Rhantus (!) consimilis, Motsch. (No. 1,500)? near No. 
944; California.—Rhantus flavo-griseus, Crotch (No. 1,501) near No. 935; North America.—Rhantus 
luteicollis, Gebl. (No. 1,502), near No. 951 ; Siberia.—Rhantus nigriventris, Motsch. (No. 1,503), near 
No. 924; Kamtschatka.—Rhantus nigropunctatus, Motsch. (No. 1,504; near No. 954); Songoria. 
