SHORT TAILS 51 
or three pairs, only in the Squillide exceeding that num- 
ber. The ganglia of the same pair are situated close to 
one another, though the commissures may stand a little 
apart. By the dorsal and lateral extension backwards 
and generally also forwards of one (or two) of the cephalic 
segments a shield or carapace is formed covering at least 
some part of the trunk and sometimes all of it. 
The above characters will suffice for a descriptive defi- 
nition of the Malacostraca, but it may be proper to remind 
the reader that the segments are sometimes so intimately 
coalesced that their separate identity is entirely obscured, 
and that moreover almost any pair of the appendages, even 
one so seemingly indispensable as the mandibles, may in 
certain cases be missing. Absence of eyes is by no means 
infrequent, and the telson, though perhaps never properly 
speaking absent, is often, by its close union with the pre- 
ceding segment, so withdrawn from recognition, that in 
practice it is spoken of as absent. 
Order 1.—Podophthalia. 
In this order there is normally a pair of compound 
eyes on movable stalks, the eyes being sometimes absent 
but never sessile; the dorsal shield or carapace extends 
back over the ninth segment or further. 
Sub-order 1.—Brachyura. 
The carapace extends over the whole head and trunk, 
with occasional exception of the trunk’s ultimate and pen- 
ultimate segments, and is longer than the pleon. In the 
carapace are excavated orbits and fossettes, hollows respec- 
tively adapted to receive the stalked eyes and the short 
first antenne. The third maxillipeds have some of the 
joints broad and flat, and they form a more or less com- 
plete operculum to the well-defined mouth cavity. The 
following pair of appendages are perfectly chelate limbs, 
commonly called the chelipeds. The next four pairs are 
adapted for walking or swimming, or rarely may have a 
prehensile character. In the sternal plastron, or breast- 
