On Aquatic Carnivorous Coleoptera or DytiscidoB. 637 



Mas, nitidus, elytvls apicem versus extenie parce subtiliter punctatis. 



Fern., minus nitida, prothorace versus latera rugoso-punctato, elytris versus basin 

 externe crebrius minute punctulatis, ad apicem fortiter parciusque punctatis. 



In the male the small palettes of the front tarsi are well developed while those on 

 the middle feet are minute and of a spongy appearance. The sexual differences of 

 sculpture are not striking, and there is apparently only one form of female. 



This species and Dytiscus hybridus have the outline of the thorax and elytra 

 more completely continuous than in any of the other allies, and the elytra are less 

 sinuate at the apex. In D. habilis the broad yellow margins of the short thorax 

 reduce the middle patch of dark colour to a transverse band ; beneath the thorax is 

 yellow with the prosternal process blackish, the metasternum in the middle and the 

 coxal processes are blackish, the large coxte being ferruginous ; the ventral segments 

 are pitchy ferruginous, with indistinct black fasciee. 



I have observed very little variation in this species. 



Mexico. 037. 



987. Dytiscus hybridus, Aube, M.C. — Subtus piceus, supra nigricans, prothorace 

 ad latera late, ad marginem anteriorem obsolete, flavo-marginato, elytris margine 

 flavo ad apicem parum dilatato et disintegrate, antennis pedibusque quatuor 

 anterioribus rufis ; angustulus, sequaliter transversim convexus; pedibus posterioribus 

 bi'evibus, robustis ; prosterni processu angusto, sat elongate, apice minute recurve ; 

 coxarum processubus parum divergentibus, rotundatis. ' Long. 27, lat. 1 4 m.m. 



Mas, nitidus, elytris ad apicem perparum punctatis. 



Fern., sat nitida, prothorace versus latera plus minusve punctate, elytris versus 

 basin externe minute punctulatis, versus apicem externe sparsim punctatis. 



The male has the small palettes on the front tarsi largely developed and of equal 

 size ; those on the middle feet are also well developed and are placed so as to leave 

 a narrow, bare, longitudinal space along the middle. The female departs but little 

 from the male, but its sculpture is variable, when most developed the punctures of 

 the thorax are connected (or rugose) and the minute punctures on the base of the 

 elytra are numerous and distinct ; when most diminished, the thoracic punctures are 

 but little connected inter se, and the basal elytral punctures are scarcely to be 

 detected. 



This species has the superficial appearance of a species of Cybister on account of its 

 short thick hind legs, its continuous outline, and rather broad and distinct yellow 

 lateral band. Except in the sculjiture of the females I have observed extremely little 

 variation. I consider it the most highly developed species of the genus. 



Eastern North America. (Massachusetts ; Pennsylvania, Kansas, Illinois, sec. Crotch). 938. 



4N3 



