184 CRUSTACEA. 



LEPTOPUS, 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 longipes. 

 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 of Leptopus, Lam., is composed 

 of several species, which, the above mentioned one excepted, accord- 

 ing to the characters here given, must be excluded from it. 



If we except some species of Hymenosomae in which the tail pre- 

 sents but four, or at most five, distinct segments, that part of the 

 body consists of six in all the following sub-genera, either in both 

 sexes, or in the males. The third joint of the external foot-jaws is 

 sometimes in the form of an inverted triangle, or of a posteriorly 

 narrowed oval, and sometimes in that of a heart. The ensuing joint 

 is inserted in the middle of its superior margin, or rather more out- 

 wards than inwards. 



Some of them, such as the three following sub-genera, approach 

 those of which we have just spoken by the almost isometrical, or at 

 least transversal form of the epistoma. 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 antennae, which does not extend be- 

 yond that of the ocular pedicles. Such is the. 



HYMENOSOMA, Leach. 



The shell is triangular or orbicular *. The species are 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 two following sub-genera, the shell is more or less convex, 

 always triangular and terminated before in a rostrum. The first 

 joint of the lateral antennae, always fixed, forms a ridge or salient 

 line between the fossulae of the intermediate antennae and that of the 

 eyes, and which is prolonged beyond the end of the ocular pedicles. 

 In the 



INACHUS, Fab., 



The tail is always composed of six segments; all the tarsi are 

 nearly straight, or but slightly arcuated ; the ocular pedicles are 

 smooth, susceptible of being concealed within their fossulse, 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 group f . 



* JJymenosoma orbicularis, Desmar., Consid., xxvi, 1. 



t Cancer dodecos ? L. ; Inachus scorpio, Fab. ; Inachus Dorsettensis, Leach, Ma- 

 lac. Brit., xxii, A ; Inachus phalanyium, Fab. ; Inachus dorynchus, Leach, Ib., 



