198 PERCY SLADEN TRUST EXPEDITION 
of pubescence, but I could not quite determine whether this was natural or due to 
abrasion; lack of material prevented my determining the sex of the specimens. 
This species is very closely allied to the Madagascan Hydrena marginicollis 
Régimbart (Ann. Soe. ent. France, Ixxi. 1903, p. 51), and may possibly prove to be 
only a variety or small local race of that species. I have been able to study a typical 
specimen of margimicollis through the kindness of M. Alluaud: it is considerably 
larger ; has the prothorax slightly more narrowed in front of the middle, and a little 
more narrowed and with sides more strongly sinuate behind the middle; the palps 
are formed in the same way, but the apex of the long 2nd joint, and the terminal 
joint, appear slightly less incrassate than in mahensis. Also marginicollis has the 
elytra a little less strongly separately rounded at the apex, and the angle between 
them (at the end of the suture) a little less deep: but the form of the elytra at the 
apex might depend on the sex, which smallness and fragility of material have prevented 
my determining either in mahensis or marginicollis. [Beneath marginicollis resembles 
mahensis : the apical part of the 5th segment of the specimen before me is nearly 
bare of pubescence, the basal part of the 6th is widely bare and smooth, while the 
apical part of the 6th has scanty pubescence. | 
Loc. Seychelles. Mahé: marshes on coastal plain at Anse aux Pins and Anse 
Royale, 19—21. I. 1909, 2 specimens. 
Hydrophilini. 
Berosus, Leach. 
Subgenus ENopturus, Hope, Col. Man., ii. 1838, p. 128. 
2. Berosus (Hnoplurus) acutispina, Fairmaire. 
Berosus acutispina Fairmaire, Ann. Soc. ent. France (sér. 4), vill. 1868, p. 196; 
Régimbart, op. cat., lxxil. 1903, p. 36; Alluaud, Liste Coléopt., p. 228. 
29, 4 9, from Aldabra. There is much variation even in this small series, specimens 
varying in length from 443—64 mm. The colour is also variable; the dark marblings 
on the posterior part of the elytra vary, being reduced in some specimens while in 
others they form a double oblique dark band with a much paler portion between its 
two parts™. 
The determination was confirmed by Monsieur Lesne, who states that he can find 
no differences between specimens submitted to him and Fairmaire’s type. Monsieur 
d’Orchymont, to whom I had previously submitted specimens, considered them to be 
the East African Berosus gracilispina Régimbart (Ann. Soc. ent. France, Ixxv. 
1906, p. 264), which may possibly be the same as Erichson’s Berosus cuspidatus from 
* Monsieur d’Orchymont called my attention to variation in the manner in which the striz meet one another 
at the apex of the elytron: he informs me that in the subgenus Hnoplurus they usually meet in the following 
pairs: 1 and 2, 3 and 8, 4 and 7, 5 and 6, 9 and 10. But in 1 ¢ and 2 9 of the Aldabra B. acutispina, the 
pairs are: 1 and 2, 3 and 4, 5 and 6, 7 and 8,9 and 10. Monsieur d’Orchymont has observed this variation also 
in specimens of B. (Hnoplurus) indicus Motsch. 
