DKCAPODA. 199 
as in the second. It would also appear that the lateral fins of the end 
of the tail resemble those of the latter. 
The remaining Crustacea of the same division differ from the jme- 
ceding in their posterior feet, which are similar to their preceding 
ones in form, proportion and uses, or equally ambulatory. They are 
also removed from them by the greater thickness and height of the 
body, the shortness of the lateral antennae, the smallness of the claAvs, 
the large eyes, and lateral fins of the tail, Avliich are composed of a 
single lamina. This tail is extended, narroAV, and simply bent under 
near its extremity. 
Megalopus, Leach. — Macropa, Latr., Encyc. 
Four species are knoAvn, three of Avhich inhabit European seas, and 
the fourth the Indian Ocean *, Avhence it AA'as sent to Paris by the late 
M. Lcschenault and INIessrs. Quoy and Gaymard. 
In our second division of the Astacini, Latr., Avill be compifised 
those Avhich haAm five pairs of false feet, the mediate antennae 
straight or nearly so, salient, projecting, and terminated by two fila- 
ments as long as their peduncle, or longer ; and Avhich, a single sub- 
genus excepted — Gebia — have the four or six anterior feet termi- 
nated by a didactyle hand. 
Their tail is ahvays extended ; their tAvo posterior feet are never 
more slender than the preceding ones, nor folded. The peduncle of 
the lateral antennae is frequently accompanied by a scale. 
Some of them, as Avell as others of the ensuing section, inhabit 
fresh Avater. 
Those in Avhich the first four feet, at most, terminate in tAVO fingers, 
Avhose lateral antennae never have a scale at the base, and Avhere 
the external leaflet of the lateral fins of the end of. the tail, presents no 
transverse suture, Avill form a first subdivision. Most of their feet 
are ciliated or pilose. They inhabit salt-Avater, and conceal themselves 
in holes Avhich they excavate in the sand. 
Sometimes the index or immoA'eable finger, formed by a projection 
of the penultimate joint of the cIravs, is very evidently shorter than 
the thumb or moveable finger, merely constituting a simple tooth. 
The 
Gebia, Leach, 
Approaches the preceding sub-genera in the tAVO anterior feet, 
which are alone didactyle. The leaflets of the lateral fins of the end 
of the tail Aviden from the base to their extremity, and are marked 
Avith longitudinal ridges. The intermediate piece or the last segment 
of the tail is nearly square f . 
Thalassina, Lat. 
The four anterior feet terminated by tAvo fingers ; leaflets of the 
lateral fins of the end of the tail narroAV, elongated, and Avitliout 
* For tlie European species, see Desmar., Consid., p. 200 — 202, and pi. xx.xiv, 2 
of the same work. 
f Thalassina litoralis, Risso, Crust., Ill, 2 ; — Gebia stellata, Leach, Malac. Brit., 
xxxi, 1 — 0, See Desmar., Consul,, p. 203, 204. 
