THE PALPICORNIA OR HYDROPHtLIDiE. 
85 
to her abdomen, and from which, in about ten days, 
the larvm are disclosed ; in a few hours another sao 
being formed. This insect formerly occurred at 
Whittlesea Mere, but was supposed to have become 
extinct in England, until it was found in some num- 
bers in 1878, in a ditch adjoining some marshy ground 
at West Ham, Essex, by Mr. T. R. Billups. It 
appears to be rare on the Continent, in spite of the 
fertility of the female. It lives in stagnant water, at 
the roots of aquatic plants. The larvae are very 
voracious, and are cannibals. 
In Helophorus and its allies the tarsi are not 
natatorial, and have the first joint very short and often 
scarcely distinct from the second. Some of them are 
slightly metallic, and most of the species live either in or 
close to the water, among stones, &c.; one or two, how- 
ever, often occur in dry places (E. rugosus, Plate VII., 
Fig. 4). The Hydrxnse and their allies, in which the last 
joint of the maxillary palpi is shorter than the penul- 
timate, frequent stones half immersed in the water or 
the water-line of muddy banks ; the species of the 
remaining genera living absolutely in tho water. One 
of these, Hydrophilus piceus, often seen in aquaria, and 
known as the “ harmless water-beetle,” is perhaps the 
largest British beetle ; the female makes a paper-like, 
pear-shaped sac, containing eggs, which is fixed on 
some aquatic plants at the surface of the water. The 
larva is, when full-grown, extremely long and stout, of 
a leathery texture, wrinkled transversely, and dirty- 
brown in colour ; the head is horny, flat on the upper 
side, and with strong projecting sharp mandibles ; 
the legs are short, and the body contracts behind, 
having two openings at the extremity of the last seg- 
