THE NEIGHBOURHOOD OF EDINBURGH. 473 
the thorax, and the number and form of the foveolets on 
its surface. But it is apparent that, in these respects, the 
insect is liable to considerable variation. In some speci- 
mens the anterior foveolet is obsolete ; and, if this circum- 
stance is to be regarded as indicating nothing more than a 
casual variety, it seems improper to make the presence of 
additional foveolets the diagnosis of specific difference. 
The diaphanous appearance of the anterior angles, and la- 
teral margins of the thorax, in E. Gibsoni, may be suffi- 
ciently accounted for on the supposition that the specimens 
were immature. The comparative depression of the thorax 
might be owing to the same cause ; and if it become eleva- 
ted as the insect advances to maturity, the probable effect 
of this will be to obliterate more or less the anterior foveo- 
lets, and by causing the margins of the ovoidal foveae at 
the base to approximate, give them the narrow and elonga- 
ted form characteristic of the typical species. In one of 
the two examples of E. viridiaeneus, which occurred in this 
neighbourhood, there were three distinct impressions on 
the anterior margin, and a fourth scarcely visible ; in this 
respect exactly intermediate between E. Gibsoni, and the 
usual appearance of E. viridiasneus. — On floating leaves in 
the pond of the Botanic Garden. May. 
Fam. HELOPHOKIDJE. 
Gen. Hydrochus. 
H. elongatus, Stepli. Hydropli. cicindeloides, Marsh, 
Not common. It occurs in a piece of stagnant water 
near the farm-house, on the north side of Braid Hills, in 
the month of May. 
H. brevis, Steph. 
A few specimens of this scarce insect were taken last 
