dilated, densely clothed beneath with glandular hairs bearing small rounded 

 palettes, fourth joint scarcely wider than the fifth, which is nearly as long as all 

 those preceding; claws equally elongate, the anterior one nearly straight and 

 feebly sinuate, the posterior a little stouter and slightly curved. Middle tarsi 

 more strongly modified, the basal joint greatly developed, convex above, con- 

 cave beneath, the basal three joints densely clothed beneath as before. Hind 

 tibiae parallel sided, slightly arcuate, with a dense fringe of erect hairs along the 

 entire length of their inner margin, the basal joint of the tarsi similarly clothed, 

 the following joints with shorter erect hair beneath, most evident on the terminal 

 joint; inner claw barely half the length of the outer. Length 13.3 mm.; width 

 7.4 mm. 



The unique type, now in my own collection, was sent me by Mr. F. S. 

 Carr, who took it at Edmonton, Alberta, June 14, 1916, "in a small 

 stream clinging to a straw." Mr. Carr writes that he has "searched 

 many miles and acres of ponds and sloughs for others, but in vain." 



This remarkable insect, perhaps the most extraordinary of our 

 North American Dytiscidae, presents to the. casual observer much the 

 appearance of our larger Ilybii more especially of Ilybius ater; on 

 closer inspection however the medially thickened antennae, the unique 

 form of the penultimate joint of the labial palpi, the strongly pro- 

 duced and deflexed apices of the hind coxal processes, the extreme 

 sexual development of the middle tarsi, and the long dense pilosity 

 of the hind tibiae and tarsi (without doubt also a sexual character) 

 at once attest its structural singularity. 



As the tribes are at present defined, it is not quite clear whether 

 our new genus should enter the Agabini or Colymbetini; there is in 

 fact a disagreement among authors as to the precise makeup of these 

 tribes. Sharp e. g. includes Ilybius in the Agabini because it agrees- 

 with the other members of the tribe in the smooth side pieces of the 

 first dorsal abdominal segment, and the presence of a row of bristles 

 at the outer apical angle of the hind femora. Zimmermann however 

 in his work on the Dytiscidae of the Berlin Museum places Ilybius 

 in the Colymbetini on the basis of the lobed apices of the first four 

 joints of the hind tarsi and the unequal metatarsal claws, disregarding 

 entirely the dorsal abdominal character' used by Sharp. It seems 

 then to be a question of deciding which characters are of greater 

 fundamental importance. In either case the relative position of Ilybius 

 remains unchanged. For obvious reasons I am unable to study the 

 dorsal abdominal segments in the unique type of Carrhydrus, but 

 it possesses the row of bristles at the apical angle of the hind femora, 

 so characteristic of the Agabini, and the apices of the metatarsal 

 joints are not at all lobed; moreover the sculpture of the surface is 

 quite like that of many Agabini and has no parallel in any of our genera 

 of Colymbetini. I am therefore at present inclined to place Carrhy- 

 drus before Ilybius and to include both in the former tribe. 



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