() J4 On Aquatic Carnivorous Coleoptera or Dytiscidce. 



Group 2. 



1015. Dytiscus bimarginatus, Say, Hydaticus bimarginatiis, M.C. — Oblougo-ovalis, 

 sat nitidud, niger, prosterno rufescente, capite thoraceque nifis, illo vertice, hoc 

 basi, nigris, elytris prope latera vitta elongata huinerali testacea, ad apicem parum 

 distincte testaceis, mavgine laterali rufescente ; aatennis pedibusque quatuor 

 anterioribus rufis. Long. 11?, lat. G^ 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 

 towai'ds the sides. 



This species is generally broader in front and less dilated behind the middle, than 

 H. rimosus, so that it is of more parallel form ; it is readily distinguished by the 

 definite and regular sublatei'al 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 otiier 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 mgro-irroratis ; antennis rufis, pedibus piceo-rufis. Long, llj, 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 is 

 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 lai'ge they are veiy 

 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. 



