654 On Aquatic Carnivorous Coleoptera or Dytiscide. 
Group 2. 
1015. Dytiscus bimarginatus, Say, Hydaticus bimarginatus, M.C.—Oblongo ovalis, 
sat nitidus, niger, prosterno rufescente, capite thoraceque rufis, illo vertice, hoe 
basi, nigris, elytris prope latera vitta elongata humerali testacea, ad apicem parum 
distincte testaceis, margine laterali rufescente; antennis pedibusque quatuor 
anterioribus rufis. Long. 114, lat. 64 m.m. 
The male tarsi and their fringing hairs are moderately well developed, the middle 
tarsi are only moderately dilated, and have a very inconspicuous basal patch of 
glandular pubescence ; the female has some coarse impressions on the thorax 
towards the sides. 
This species is generally broader in front and less dilated behind the middle, than 
H. rimogus, so that it is of more parallel form ; it is readily distinguished by the 
definite and regular sublateral yellow stripe on the wing-cases. It exhibits some 
sexual differences in form and colour, the females being generally rather narrower in 
front than the males, and they are liable to have the black colour of the thorax 
more extended and diffused, on the other hand they have the yellow sublateral band 
of the wing-cases more elongate. 
North America. 1031. 
1016. Hydaticus rimosus, Aube, M.C.—Ovalis, nitidus, niger, prosterno anterius 
rufescente, capite thoraceque rufis, illo vertice et signatura inter oculos, hoc in 
medio, nigro-umbrosis ; elytris ad latera irregulariter testaceo-signatis, signaturis 
illis nigro-irroratis ; antennis rufis, pedibus piceo-rufis. Long. 11s, lat. 6 m.m. 
The male tarsi are moderately developed ; the female has some coarse impressions 
on the lateral parts of the thorax. 
In this species the limits between the black and red colours of the thorax are 
very indefinite, on careful examination it is seen that this black shading arises from 
a large basal black cloud, and from another discoidal cloud confused with it. The 
yellow marks on the elytra are irregular, indefinite, and variable, there is a small 
humeral mark having a greater or less extension backwards, the outer margin Js 
yellow, and this yellow margin becomes reddish in front, but does not reach to the 
base, at the apex it is much dilated, and behind the middle it has one or two yellow 
small marks connected with it, when these yellow marks are large they are very 
irregular and much broken up by black dots or divisions, sometimes the humeral 
mark gives off in the direction of the scutellum the beginning of a transverse 
band. 
Cuba, Guadeloupe, Mexico. 1030. 
