DECAPODA. 
179 
notched ; two teeth on the posterior margin, and two others 
widely separated on each lateral muscle ; the posterior lai'gest 
and sjjiniform, and situated above the origin of the posterior 
feet. 
I'he sea coast of the western departments of France produces 
some other species, Avhich belong to the genus Ebalia, Leach *. 
All the remaining ones are from India and America. 
Some fossil Leucosise are found in the East Indies. Three 
species have been described by M. Desmarest, two of which, 
according to him, are true LeucositE, Leach, and Avhich are 
now living in the same countries, and peculiar to them. 
Our fifth section, that of the.TRiGONA, is composed of those species 
whose shell is usually triangular or subovoid, narrowed before into a 
point or kind of beak, generally uneven and rough, with lateral eyes. 
The interval comprised between the antennee and the buccal cavity 
is always nearly square, as long, or almost as long, as broad. The 
claws, at least those of the males, are always large and elongated. 
The following feet are very long in a great number, and sometimes 
the two last even differ in form from the preceding ones. The third 
joint of the external foot-jaws is always nearly square or hexagonal, 
in those at least whose feet are of the ordinary length. 
The apparent number of the caudal segments varies. In both 
sexes of several it is seven ; in others, however, the males at least, it 
is less. 
Several of these Crustacea are designated by the vulgar appellation 
of Araignees de mer or Sea-spiders. 
Although the species of this tribe are very numerous, but two 
have as yet been discovered except in a fossil state, one of which at 
least — Maia squinado — exists at the present day in a living state, and 
in the same localities f. 
A first division will comprehend those whose second and following 
feet are similar, and which diminish progressively in size. 
From the latter we will form a first group of all those where the 
tail, either in l)oth sexes, or in the females alone, is composed of seven 
segments. The third joint of the external foot-jaAVS is almost 
always square, and truncated or notched at the superior internal 
angle. 
Very large claws, particularly so Avhen compared Avith the other 
feet, Avhich are extremely short, directed horizontally and perpendi- 
cularly to the axis of the body, as far as the carpus or joint immedi- 
ately preceding the hand, then reflected anteriorly on themselves Avith 
the fingers bent, suddenly forming an angle ; very short ocular pedi- 
cles, projecting but little, if at all, from their cavities ; a stony and 
very uneven or spiny shell, designate the 
Partiienope, Fab. 
The lateral antennae of some are very short, not exceeding the 
♦ Malac. Brit., xxv. 
t See Desmar., Hist. Nat, des Crust. Foss. 
N 2 
