212 ADEPIIAGA. 



with the corneous parts pale yellowish ; the head is oval, rather elongate, furnished 

 with two strong jaws, and two short and thin 4-jointed antenua3 ; the three anterior 

 segments of the body bear each of them a pair of rather slender legs about erjual in 

 length to the appendages above referred to; the eggs are laid on aquatic plants; they 

 hatch in about eight days; when the larva has attained its full size it creeps out of 

 the water and spius a whitish cocoon on the stems of rushes or other aquatic plants ; 

 in about a month the perfect insect emerges, and immediately returns to the water ; 

 the cocoous of Orectochilus have been found beneath willow bark a yard from the 

 edge of a river and two feet above the ground; this species iu the perfect state affects 

 logs and submerged timber much more than Gi/rlniis. Some of our British species of 

 Gi/rimis are very hard to distinguish, and it seems to bo in several cases a matter of 

 opinion whether they are regarded as species or as varieties ; all students of the group 

 .should read Dr. Sliarp's excellent monograph " On the British GyrinidaB " in the 

 Entomologist's Monthly Magazine, v. 52 ; several of his views there expressed he has 

 since modified ; the arrangement below appears to represent the present state of our 

 knowledge on the subject, but must in one or two cases be regarded as provisional. 



It will be noticed that one of the most important characters on which 

 the species is separated is the colour of the epipleurte or reilexed margins 

 of the elytra; care must, however, be taken , to see that the specimens 

 examined are mature, and they should be turned upon their backs and 

 looked at from above ; if viewed sideways when mounted on card the 

 reflection from tlie card and the red legs is quite sufficient to cause the 

 shining bronze margins of the marinus group to appear reddish ; in 

 immatitre specimens also they have a reddish tint, but this is (piitc 

 difl'erent from the clear red colour of the natator group. 



I. Under surface entirely red. 



i. Scutellum with a small keel-like projection ; 



elytra unicolorous ; length 4 mm G. MINTJTtrs, F. 



ii. Scutellum without projection; punctures of 

 elytra usually situated on more or less distinct 

 metallic lines; length 6-7 mm G. UUINATOK, ///. 



II. Under surface either entirely dark, or (iu some 



varieties) partially red. 

 i. Retlexed margins of elytra red. 



1. Form elongate more or less parallel-sided ; 



length 5-7i mm. 



A. Apex of elytra transversely truncate with 

 the external angle sharply marked ; length 



5-6^ mm G. elongatfs. Aide 



{distinct us, Sharp). 



B. Apex of elytra truncate in a curve with the 



external angle not marked ; length 6-7j mm. G. BICOLOE, Fai/k. 



2. Form oval ; length 5-6 mm. 



A. Interstices of elytra and upper surface of 

 head and thorax covered with tine punctures 



or strise G. caspifs, 3Ien. 



(v. colj/inbtis. Sharp's Cat.). 



B, Interstices of elytra smooth ; punctures 



and margins more or less brassy . . . . G. NATATOE, Scop. 

 ii. Beflexed margins of elytra pitchy red; punctin-es 



not brassy ; interstices of elytra smooth ; length 



_ 'lAunn G. SvFyRlAm, Scriba. 



iii. Beflexcd margins of elytra bronze ; interstices 



of elytra finely punctured. 



