THE STALK-EYED CRUSTACEA. 255
species, Thia polita, curiously enough, does not belong to this
group, but is a true crab.
The Shrimps (Crangonidae) and Prawns (Palaemonidae) are
most interesting animals and are well represented on the Essex
coast. The true Shrimp, Crangon vulgaris, may he at once
recognised by the flat cephalo-thorax and its sand-like colour.
It is the "Brown Shrimp" because it does not turn red on being
boiled like the prawn under like treatment.
[Mr. Lovett made the following observations in the Zoologist
for 1885, pp. 468—9, which we have often verified when noticing
shrimps in the sea-rivulets on our Essex coast :—"The colour of
this species is grey or brownish-grey, speckled with darker cells
of pigment, but, of course, like many crustaceans, this colour
varies according to the habit of the specimens ; for those from a
light sandy bottom are paler and slightly yellow, whereas those
from a muddy estuarine locality are dark and dirty looking : in
fact, so completely does Crangon vulgaris resemble in tint the
bottom on which it lives, that it is absolutely impossible to detect
it when motionless. I have frequently observed this in shallow
clear water where shrimps almost covered the sand ; and yet,
when not actually moving, not an outline could be traced or
a single living thing seen, but on alarm hundreds of little
flashes showed where these thoroughly invisible tiny things
really were."]
Several other species of the genus Crangon occur on the
Devon and Dorset coasts, but are rather rare. Alpheus ruber, a
rare and brilliantly coloured species is found at Herm in the
Channel Islands. This animal possesses the power of making a
sharp clicking sound by means of a spine at the base of the first
abdominal segment ; much in the same fashion as that of the
"skip-jack" beetle. Athanas nitescens is another somewhat rare
species from Jersey, as also is Hippolyte spinus.
Pandalus annulicornis is really a "prawn" and is a typical
Essex form. It is in fact the "Red Shrimp" of the Thames
excursion steamers. It works the tide up and down for its food,
and is a most useful scavenger. The term "Red Shrimp" is
applied to several diverse species round the coast. At South-
hampton I saw Palaemon squilla (the small prawn) hawked about
under this commercial name, and P. varians, where it occurs
commonly, is also so called.