SHARP : HYDRADEPHAGA OF LANCASHIRE AND CHESHIRE. I99 
Lepidoptera as Detlephila galit and Coltas edusa, and owe their origin 
to a similar set of factors, and in the case of Hydradephaga we can 
hardly seriously invoke the agency of migration to explain what we 
cannot understand, as has been done in the case of the Lepidoptera. 
For instance, 1888 was notable for Ayphydrus ovatus. All the 
ponds swarmed with that species ; since then, they have only occasion- 
ally been met with. In 1889. Agabus sturmii was unusually 
abundant ; in 1890 the Celambii versicolor and inegqualis took the 
lead, and also this Laccophilus hyalinus ; while last year, Hydroporus 
lineatus, a beetle usually rather scarce, was particularly plentiful. 
Only a careful study of atmospheric conditions and meteorological 
records, over a long course of years, combined with a series of 
accurate observations on greater and less abundance could, I think, 
furnish us with any sort of tenable aoe to account for these 
phenomena. But this is a work as yet untrie 
But passing into the next group of genera, we commence i 
Fydrovatus (Oxynoptilus in Dr. Sharp's Catalogue). There is only 
one species, and that has only been taken in one pond near 
Portsmout 
The three genera, Bidessus (compressed or well bound), Celambus 
(scooped out), and Deronectes (swimmer), are usually all included in 
the great genus Aydroporus ; but Canon Fowler, with very good 
reason, separates them. They are four entirely distinct types 
of insect, and the old genus Aydroporus was always cumbrously 
large. 
The three species of Bidessus are small rounded beetles, all very 
rare, and none so far taken in our district. 
flyphydrus, which has always been a distinct genus, has one 
species; an insect which to mistake is impossible. It is a dark 
orange-red colour, and almost globular. It is fairly common in all 
the Cheshire ponds, and was especially so, as mentioned above, in 
the summer of 18 
Celambus has eight species 
C. reticulatus (versicolor) is common in the district, but more local 
and erratic than C. inegualis, and it also appears rather earlier. 
C. luceratus is recorded by Mr. Gregson from Bromborough, 
Cheshire. 
C. parallelogrammus 1 have taken once ina peaty pool in Delamere 
Forest. It is rather a scarce species, and does not seem to have 
been otherwise recorded in the district. The other three species are 
not recorded, so we have five out of eight in this genus 
We now come to Deronectes with five species, all fine distinguished 
looking insects, with a certain rotundity of outline and dilation of 
July 1892. 
