1914.] 131 



15 (14) External apical angle of elytra quite rounded 6, bieolor. 



16 (5) Inflexed margin of elytra metallic. 



17 (18) Claws of middle and hind tarsi yellow 9, opacus. 



18 (17) Claws of middle and hind tarsi black. 



19 (20) Size larger, J 6, 9 7 mm. long 10, marinus. 



20 (19) Size smaller, J 5, ? 6 mm. long 11, edwardsi. 



1. Gr. mintttus, Fabr. 



This species has been made the exponent of a subgenus Gyrinulus 

 on account of the elevation on the scutellum. This character readily 

 distinguishes the insect from all our other Gyrini. The pronotum of 

 G. minutus is remarkably dull, but there is a fine shining line along the 

 middle, and the scutellar elevation looks like a prolongation of this line. 

 The a3deagus (figs. 1) differs but little from that of G. natator, but 

 there is not so much chitinisation of the tip of the ventral surface of 

 the median lobe. 



The species is a local one, but occurs throughout Great Britain 

 and Ireland, as I am informed by Mr. Balfour Browne. 



2. Gr. TTRINATOR, Illig. 



This species is distinguished by the under surface being entirely 

 yellow or red, and by the very smooth upper surface, the serial punc- 

 tures near the suture being effaced and, as it were, covered by a sub. 

 stance that forms lines of coppery effulgence. The sedeagus (figs. 2) 

 is very like that of G. natator, but the median lobe is gradually and 

 regularly narrowed from its broadest point near the base of the bulb, 

 to the tip which is truncate : there is no chitinisation of the ventral 

 face at the extremity. 



3. G-. natator, L. 



This, the most ubiquitous of our species of Gyrinus, may be 

 recognised by its bright parti-coloured under surface, its broad definitely 

 oval form, and the great delicacy of the series of punctures on the 

 elytra near the scutellum, the oblique double series of punctures at the 

 apex of each elytron is always moderate — never much obliterated, never 

 very coarse and deep. Some of the individuals of G. elongatus approach 

 it very closely, but in no case is that species so broadly oval, the elytra 

 in it being always straighter at the sides, with the outer apical anglj 

 less deflexed and obliterated. 



As regards variation ; in this country the specimens invariably have 

 the mesosternum and the last ventral segment bright red. It is said 



