254 PERCY SLADEN TRUST EXPEDITION 



A single specimen, which agrees with Dr Sharp's type of H. humilis : it is darker in 

 colour, the elytra being so dark throughout that the suture does not appear any darker 

 than the rest of the surface. Rdgimbart (I.e.) considers H. humilis to be a variety of 

 H. sordidus Sharp, which is known from Egypt, Arabia &c. 



Log. Aldabra : " Wilson's Well," Takamaka, x. 1908 (Fryer). Madagascar. 



BiDESSUs Sharp, On Dytiscidse, p. 344. 

 I. Species with a distinct sutural stria. 



44. Bidessus thermalis (Germar). 



Hydroporus thermalis Germar, Faun. Ins. Eur., 20. 3. 



Bidessus thermalis Sharp, On Dytiscidse, p. 353 ; Regimbart, Mem, Soc. ent. 

 Belgique, iv. 1895, p. 85. 



11 specimens, varying in length between 1*5 and 1*9 mm. They are of a rather 

 small form, apparently approaching somewhat to the var. signatellus Klug. There is 

 some variation in colour ; the dark marks at the base of the pronotura and elytra are 

 almost absent in some specimens; the inner dark band on the disc of the elytron is always 

 characteristically dilated outwards in the form of a hook at its posterior extremity and in 

 its anterior part is sometimes confluent with the shorter outer band, sometimes distinctly 

 separated from it. Ventrally the sterna and posterior coxae are ferruginous, while the 

 abdomen excepting at its extreme base and apex is much darker. 



Loc. Chagos Islands : Diego Garcia, 1905 : 8 of the specimens are labelled by T. B. 

 Fletcher " 9. VII. 05. In stagnant pool in Barachois." The species is known in various 

 forms from S. Europe, N. and W. Africa, Egypt, Arabia, Persia, and Bengal. 



45. Bidessus capitatus, Regimbart. 



Bidessus capitatus Regimbart, Mem. Soc. ent. Belgique, iv. 1895, p. 83 ; AUuaud, 

 Liste Coldopt., p. 59. (PI. 12, fig. 14.) 



Var. ? 57 specimens from Aldabra. Length from just under 2 to 2^ mm. Head 

 and prothorax reddish-fulvous, the former infuscate behind and along the inner margins of 

 the eyes, the latter very narrowly darker along its fi-ont margin, broadly darkened behind 

 between the plicae. Head with a slight transverse elevation at the base of the clypeus, 

 finely punctured : pronotum with fine and rather numerous punctures, stronger towards 

 the base : plicae oblique continued on to the elytra as slightly longer grooves. Elytra 

 rather densely and rather strongly punctured, with fine pubescence ; fuscous, with the 

 following pale (yellowish-testaceous) markings : the lateral margin, which is sometimes 

 divided behind the middle by an elongated dark mark and triangularly dilated at the 

 apex ; two longitudinal vittae on the front part of the disc, neither of them reaching the 

 base, the inner usually shorter and ending posteriorly before the middle of the elytron, 

 the outer longer and ending behind the middle of the elytron : these longitudinal pale 

 vittae are connected in front with one another and with the lateral margin by a transverse 

 pale vitta running obliquely from the shoulder to near the sutural stria. The sutural 

 area, between the sutural stria and the suture, is dark throughout its length : it, and 



