184 
CRUSTACEA. 
Leptoi'us, Lam. 
Tail of the females composed of but five segments; the body con- 
vex and feet very long. 
But a single species is known which is part of the collection of the 
Museum d’Histoire Naturelle, where it is called Maia loiigipes. 
Doctor Leach proposed to designate this genus by the name of Ste- 
nopus, a denomination we have not adopted, inasmuch as it is al- 
ready appropriated to another. That (jf Leptopus, Lam., is composed 
of scA'cral species, Avhich, the above mentioned one excepted, accord- 
ing to the characters here given, must he excluded from it. 
If Ave except some species of Hymenosomae in Avhich the tail pre- 
sents but four, or at most five, distinct segments, that part of the 
body consists of six in all the thlloAving sub-genera, either in both 
sexes, or in the males. The third joint of the external foot-jaAA's is 
sometimes in the form of an inverted triangle, or of a posteriorly 
narroAved oA'^al, and sometimes in that of a heart. The ensuing joint 
is inserted in the middle of its superior margin, or rather more out- 
Avards than iiiAvards. 
Some of them, such as the three folloAving sub-genera, approach 
those of AAdiich AA'e have just spoken by the almost isomctrical, or at 
least transversal form of the eifistoma. The base of the intermediate 
antennae is but a short distance from the superior margin of the 
buccal cavity. 
One of these sub-genera is distinguished from the others by the 
flatness of the shell, and by the superior extremity of the first joint 
(free in several) of the lateral antennse, Avhich does not extend be- 
yond that of the ocular pedicles. Such is the. 
H YMENOSOMA, Leach. 
d'ho shell is triangular or orbicular *. The species arc generally 
small and peculiar to the Indian Ocean and coast of Australia. The 
number of caudal segments varies, but never extends beyond six. 
In the tAvo fulloAving sub-genera, the shell is more or less convex, 
ahvays triangular and terminated before in a rostrum. The first 
joint of the lateral anteniice, ahvays fixed, forms a ridge or salient 
line betAveen the fossulse of the intermediate antennae and that of the 
eyes, and AAdiich is jirolonged beyond the end of the ocular pedicles. 
In the 
Inachus, Fab., 
The tail is ahvays composed of six segments; all the tarsi are 
nearly straight, or but slightly arcuated ; the ocular pedicles are 
smooth, susceptible of being concealed Avithin their fossulte, and 
there is a tooth or spine, at least in the males, at the posterior extremity 
of the latter cavities. Doctor Leach has considerably reduced the 
original extent of this groii]) +. 
* Hijmenosoma orbimluris, Desmur., ConsicL, xxvi, 1. 
t Cancer dodecos ? L. ; [nachus scorpio, Fab. ; — Ina' Ims Dorset lensis, Leach, Ma- 
lac. Brit., xxii, A ; — Inachus phakuujium, Fab. ; Inachus dorynchus, Leach, Ib., 
