674 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



Fern., elytris sulcis latis, villosis, integris. 



The male characters in this species are the same as in l)3'sticus sulcatus. 



The species indeed is very closely allied to the D. sulcatus, but remains always 

 perfectly distinct ; it is smaller, and appears narrower, the anterior of the three 

 black marks on the head is wanting, the black colour is less developed on the 

 ventral segments, and the liind legs have the femora entirely yellow, and the tibiae 

 and tarsi more or less rufescent, never black. In the female there is very slijj;ht 

 development of the pubescence on the thorax, and the third furrow is narrower, 

 owing to the elevation which limits it externally being more deflected from a 

 straight course than it is in D. sulcatus ; and the furrows, especially the inner one, 

 are continued a little nearer to the apex. The species varies in the colour of the 

 lower surface, which is sometimes entirely yellow. 



Eui-opeaad Siberia; from Sweden and Finland, 68° 30' (Sahlberg), to Spain. 



1054. Acilius semisulcatus, Aub^, Spec. p. 132.— Vix latus ; supra parum convexus, 

 testaceus, capite prothoraceque signaturis transversis nigris, elytris creberrime 

 nigro-irroratis pone medium fascia pallida plus minusve distincta ; subtus pectore 

 nigro, abdomiue nigricante, maculis lateralibus fasciisque transversis testaceis, 

 pedibus testaceis, femoribus posterioribus basi plaga nigricante ; corpore creberrime 

 punctato ; antennis elongatis, tenuissimis. Long. 13, lat. 7i m.m. 



Mas, parura nitidus, elytris creberrime punctatis. 



Fern., elytris sulcis latis setulosis, ad basin plus minusve abbreviatis, suturali 

 semper breviore. 



The male has the front tarsi much as in the preceding species ; on the middle 

 tarsi the tufts of hairs at the inner edge of the three basal joints are elongate and 

 distinct, but there is never any development of small palettes on the lower surface. 



The larger specimens of this species present a great resemblance to the smaller 

 ones of D. oanaliculatus. A. semisulcatus is, however, narrower, and has the 

 epipleurae considerably less developed, and the cilias at the posterior margins of the 

 joints of the hind tarsi more elongate. 



The species shows a gi-eat deal of variation. The form ordinarily found in the 

 Eastern United States may be considered as the typical one ; the specimens from 

 these parts differ only moderately in size, colour, and sculpture, except that a 

 variety occurs in which the whole of the lower surface is clear yellow. Tn North- 

 west America there is found a form appearing at first very distinct, and making 

 the greatest approximation to the European D. canaliculatus. These specimens are 

 larger, more particularly the females, and the individuals of this latter sex have 

 the three outer grooves continued almost to the very base of the elytra, while the 

 costse between the grooves are naiTower and more abruptly defined, particularly in 

 front, and the punctuation near the sides of the thorax is rougher ; in the males 



