674 On Aquatic Carnivorous Coleoptera or Dytiscide. 
Fem., elytris sulcis latis, villosis, integris. 
The male characters in this species are the same as in Dysticus 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 hind legs have the femora entirely yellow, and the tibize 
and tarsi more or less rufescent, never black. In the female there is very slight 
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. 
Europe and Siberia; from Sweden and Finland, 68° 30’ (Sahlberg), to Spain. 
1054. Acilius semisulcatus, Aubé, 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, abdomine nigricante, maculis lateralibus fasciisque transversis testaceis, 
pedibus testaceis, femoribus posterioribus basi plaga nigricante ; corpore creberrime 
punctato ; antennis elongatis, tenuissimis. Long. 13, lat. 74 m.m. 
Mas, parum nitidus, elytris creberrime punctatis. 
Fem., 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 joimts 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. canaliculatus. A. semisulcatus is, however, narrower, and has the 
epipleure considerably less developed, and the cilie at the posterior margins of the 
joints of the hind tarsi more elongate. 
The species shows a great 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. In 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 
costee between the grooves are narrower and more abruptly defined, particularly in 
front, and the punctuation near the sides of the thorax is rougher; in the males 
