DECAPODA. 
421 
is always prolonged into a point, often forming a sharp-pointed plate, very much compressed, and 
toothed on both edges. The antennm are always advanced ; the lateral ones generally very long, and 
in the form of a very slender thread : the intermediate antenme, in the majority, are terminated by 
three filaments. The eyes closely approach each other. The outer foot-jaws, longer than ordinary, 
resemble palpi or antennae. One of the two fore pair of legs is often folded back, or doubled. The seg- 
ments of the tail are dilated laterally. The outer plate of the terminal swimmeret is always divided in 
two by a suture, as in the terminal species of the preceding section. The middle piece, or the seventh 
and last segment of the tail, is long, narrowed towards the tip, and is armed above with rows of small 
spines. The false legs, of which there are five pairs, are long and foliaeeous. These Crustacea are much 
eaten in different parts of the world, and some species are salted for keeping.* 
Those wliich liave the three anterior pairs of legs didactyle, the length gradually increasing, so that the third 
pair is the largest, compose the genera Penceus, Fabr., (having no annular divisions in the joints of the legs, and 
composed of numerous species, one of which, the Caramote (P. sulcatus, Oliv.), is very common in the Mediter- 
ranean, and is a great object of commerce, being salted for exportation to the Levant, and of which the English 
species (P. trlsulcatus, Leach) is considered by Latreille to be a local variety),— and Stenopiis, Fabr., having the two 
penultimate joints of the four posterior legs with annular divisions. 
The remaining species have not more than the two anterior pairs of legs didactyle, and the intermediate antennse 
terminated by three filaments. 
Atya, Leach, formed of a single North American species, A. scahra, is anomalous in the form of its four claws, 
which are small, and split to the base with long terminal pencils of hair, the preceding joint being crescent-shaped. 
The others have the claws of the ordinary didactyle form. These, with the exception of the terminal genus, have 
the legs more or less robust, but not filiform, without any appendage at the base. The body is neither very soft, 
nor very much elongated. 
Crangon, Fabr., has the fixed finger or index of the two anterior and largest claws reduced to a small tooth, the 
moveable finger being hook-shaped. The superior or intermediate antennae have only two terminal filaments ; the 
second legs are folded, and more or less distinctly didactyle at the tips ; none of the joints are annulated ; the 
rostrum is very short. Crangon vulgaris, Fabr., the Common Shrimp, is the type of this genus. It does not 
exceed two inches in length, and is of a pale glaucous green colour, dotted with grey. It is caught throughout 
the year with the assistance of circular nets. Its flesh is delicate. 
PontopMlus, Leach {Egeon, Risso), does not generically differ from Crangon. 
\ Processa, Leach (Nika, Risso), has one of the fore-legs terminated in a point, and the other didactyle. The 
second pair of legs are of unequal length, one being very long, with the two joints preceding the claw annulated. 
N. edulis, Risso, found at the mouth of the Rhone. 
Hymenocera, Latr., differs in the proportions and form of the legs. 
To these succeed a number of genera in which the legs and claws do not present any anomalous structure, and 
in which the superior or intermediate antennas have only two terminal filaments, including the genus Ilippolyte, 
Leach, comprising several British species of shrimps, and in which the four fore-legs 
are terminated by a didactyle claw, the second pair being longer than the first ; and 
Pandalus, Leach, comprising another British species (P. annulicornis, Leach), in 
which the fore-legs are [very small and] simple, or scarcely bifid; the two following 
long, of unequal length, with the two joints preceding the claw annulated. 
The Prawn is the type of the genus Paltemon, which differs from the last group 
of genera in having the upper antennae terminated by three filaments. It has 
I the two anterior pairs of legs didactyle, the smaller pair being folded ; and the carpus is not articulated. The 
ji rostrum is very long [and spined]. Some of the exotic species acquire a very large size, with the second pair of 
I; legs very long. The flesh of the common species is more esteemed than that of the Shrimp. According to M. 
de Brebisson (Cat. Meth. Crust. Depart, du Calvados), they are caught in the same manner as Shrimps, but only 
i in summer. They swim well, especially when alarmed, and in different directions. They frequent the coast. The 
; lithographic stone of Pappenheim and Sohlnofen often contains the remains of a fossil species, which Desmarest 
ji names Paltemon spinipes. Another fossil species, but of a much larger size, has been found in England. Tl'he 
species ordinarily sold in the fish-shops is the Paltemon serratus. It is generally three or four inches long, and of 
1 a pale red colour, which is brightest in the antennae, and especially in the swimmeret of the tail. Its frontal spine 
j! extends beyond the peduncle of the middle antennae : it is curved upwards at the tip, with seven or eight spines 
!, above, and five beneath. One of the sides of the body is often distended, which is caused by a parasite of the 
genus Bopyrus beneath the carapax, affixed to the branchiae. Paltemon squilla, Linn., is another but smaller 
Fig. 7 — Ilippolyte varians. 
' * [The gradual developenient of several species of Carides (Pake- 
monidae) has been recently described by Dr. J.V. Thompson in Jame- 
son’s Edinb. Phil. Journ., Oct. 1836, and by Captain Ducane in the 
I Annals of Nat. Hist ., On 6rst bursting from the egg, the 
tail is terminated by a spatulated plate, destitute of lateral as well as 
! subabdominal appendages; the rostrum is produced into a simple 
point ; the lateral antennae exhibit only the large scale ; and only two 
fi of the legs are of the ordinary length, and these are bihd, as in the 
Schizopods ; the other legs are very minute, and incurved. In the 
ii course of several moultings, the antennse are lengthened ; the rostrum 
and ridge of the carapax spined ; the five pairs of legs extended to 
their full size, but still bifid ; and the subabdominal appendages and 
the swimmerets gradually developed. These observations are as- 
serted, by M'Leay and others, to afford a complete confirmation of 
the correctness of Thompson’s assertions that Zoea is the larva of the 
common Crab, and that all the Crustacea undergo transformations, — 
these gentlemen overlooking the fact that Zoea is a Decapod animal, 
not furnished with bifid legs, but having the two pairs of outer foot- 
jaws immensely developed, but of the ordinary Macrourous construc- 
tion, as are the internal parts of its mouth.] 
