of DytiscidcB Darwiniancs. 3 



genus by the great thickness and different form of the joints of its 

 external maxillary and labial palpi, the slender short terminal 

 joint of the internal maxillary, and its very short thick and cu- 

 riously jointed antennae. 



In conclusion, I beg to express my great obligation to the Rev. 

 F. W. Hope for the free use of his cabinet and library, and to 

 J. O. Westwood, Esq., for his kind assistance in making the dis- 

 sections and drawings for this paper. 



DYTISCIDiE DARWINIANS. 



Cybister, Ciirf. 



1 . C. 2-Hngtilatus, Bab. 



Olivaceo-niger, capite antice thoracis elytrorumque lateribus 

 rufis ; elytris postice latioribus impunctatis, sterni laciniis 

 spathulatis ; pedibus 4 anticis rufis, posticis bruneis, rufo-cili- 

 atis, omnibus 2-dactylis. (Long. corp. 12-14; lat. 7-8|. lin.) 



Olive black, ovate. Head olivaceous, with its anterior margin 

 rufous; two small black foveas in front, and two slender black lines 

 extending diagonally from the antennae towards the crown ; no 

 frontal lunule ; impunctate except when greatly magnified, but 

 then it is found to be, together with the thorax and elytra, covered 

 with extremely minute punctures ; labrum rufous ; palpi and an- 

 tennae ferruginous. Thorax with an interrupted row of impressed 

 dots on its anterior margin, an oblique one on both sides, and an 

 abbreviated longitudinal dorsal channel, the lateral margins broadly 

 rufous. Scutellum olivaceous ; elytra ovate, posteriorly dilated, 

 the exterior margin rufous, three rows of distant punctures upon 

 each, and an irregular row of more minute ones on the exterior 

 margin. Under side black, with a bright yellow spot at the pos- 

 terior angles of the hinder sutures. The four anterior legs ru- 

 fous, very short ; posterior short and thick, particularly the tibiae, 

 dark ; all the tarsi with two claws, but both those of the hinder 

 pair appear to be immoveable, fringed internally with long rufous 

 hairs. (Plate I. fig. 1 a, last joint of hind tarsi seen above; 

 1 b, ditto seen beneath.) 

 Hab. Maldonado, on the north coast of the Rio del Plata. 

 A forma typicali (C Roeselii) hujusce generis insecta nostra 

 differe videntur articuli basalis palporum maxillarium exter- 

 norum antennarumque longitudine majori, elytris scrobiculatis 

 foeminae, mandibulis brevibus truncatis et oblique emargina- 

 tis tarsisque posticis ungulis duobus instructis. 



B 2 



