DECAPODA. 
415 
and ciliated. Tlie tail is composed of seven seginents, but three of them are confluent in the males. The type 
is Cancer personatus, Herbst., found upon the coast of England. [This genus is of very difficult location, and has 
little real relation with Leucosia : it is more nearly allied to some of the arcuated species.] 
Leucosia,Y&h., has the carapax of variable form, but generally globular or ovoid, and as hard as stone; the 
lateral antennae and eyes are very small ; the tail, large and suborbicular in the females, is generally composed of 
four or five, but never of seven segments. Dr. Leach cut up this genus into many others. A very few species 
belonging to his genus Ebalia are found on the English coast. The majority of the family inhabit tropical seas. 
The fifth section, Trigona, is of very great extent, and consists of species having the carapax 
generally irregular or subovoid, and narrowed in front into a kind of beak ; ordinarily very rough and 
uneven, with the eyes lateral. The epistoma, or space between the antennse and oral cavity, is always 
nearly square, and as long as broad. The claws, at least of the males, are always large and long. 
The following legs are very long in the majority, and occasionally the posterior pair have a form dif- 
ferent from the preceding. The apparent number of joints in the tail varies, being seven in both sexes 
of the majority of species ; but in others, at least in the males, it is less. Many of these crabs are 
commonly called sea spiders. Although the number of species of this section are very numerous, only 
tM'O had been discovered in a fossil state ; one of which, Maia Squinado, exists at the present time in 
the same localities. 
Latreille divides this section into sub-sections, from the number of joints in the tail, and the form of the joints of 
the foot-jaws. Amongst those with the tail, either in both sexes, or in the females, composed of seven segments, 
Parthenope, Fabr., is distinguished by the immense size of the claws, and the smallness of the other legs ; the 
fingers are suddenly bent downwards, the ocular peduncles very short, and the carapax exceedingly rough. 
A species found on the coasts of England and France (Cancer asper. Pennant) forms the genus Eurynome, Leach ; 
the tail is seven-jointed. The other species of Parthenope are found in the Indian ocean. 
Maia, Leach, has the fingers not deflexed ; the anterior pair of legs scarcely thicker than the others, which are 
moderately long ; the carapax has two frontal spines, and its back and sides are also armed with many tubercles 
and spines. The typical species. Cancer Squinado, Herbst., is very common on the coasts of France and the 
Mediterranean. It is one of the largest of our crabs, and was known to the ancient Greeks under the name of 
Maia, being sometimes figured on their medals. [By the fishermen it is called the Thorn-back, or King Crab.] 
Another common British species is the Cancer araneus, Lin., belonging to Leach’s genus Hyas, having the 
carapax elongate, subtriangular, subtubercled, with the lateral margins dilated into a lanceolate projection, ex- 
ternal antennae with the first joint dilated. 
Amongst the species, which have not more than six abdominal segments, and the legs generally long and 
filiform, and the third joint of the outer foot-jaw narrower than in the preceding subsection, Hymenosoma, 
Leach, has the carapax triangular or orbicular, depressed [and soft], and the basal joint of the lateral antennae 
does not reach beyond the ocular peduncles. The species are small, and found in the Indian and Australian seas. 
The British genera, Inachus and Achceus, have the carapax subconvex and triangular, and their abdomen six- 
jointed. Their four pair of posterior legs are very long, especially the pair succeeding the claws. In the latter 
I respect the British genus Stenorhynchus, Latr. (Macropodia, Leach), closely resembles them, having also the tail 
six-jointed in both sexes, and the front of the carapax notched. The type is 
the very common Cancer Phalangium, Pennant. The genus Pactolus, Leach, 
characterized by having the four hind-legs furnished with a didactyle claw [has 
been found by M. Milne Edwards to have been constructed upon a fictitious speci- 
men in the British Museum]. 
Lithodes, Latr., is at once distinguished by having the hind pair of legs so small 
as to appear almost abortive. The type is a large crab of rare occurrence in British 
seas, named Cancer Maia, Linn. The tail is membranous ; the outer foot-jaws are 
elongated and apart ; the carapax is triangular, very spinous, and terminated in a 
toothed spine. [This is a very anomalous genus, whose relations are difficult to 
j Fig. 3.— Stenorynchus Phalangium. decide.] 
I [Professor Bell and De Haan have described many new and curious genera belonging to the section Trigona : 
[ the former, in the second volume of the Transactions of the Zoological Society ; and the latter, in his work upon 
the Crustacea of Japan.] 
The sixth section, Cryptopoda, is composed of a few species remarkable for having the legs, 
except the anterior pair, concealed, when folded up, beneath the dilated lateral margin of the carapax, 
I which is nearly either semicircular or triangular; the upper edge of the claws is compressed, and 
' formed like a cock’s comb. The species are exotic, and compose the two genera Calappa, Fabr., and 
' AEthra, Leach. In the shape of their claws they resemble some of the Arcuata and Pinnipedes, such as 
Hepatus, Mursia, &c. ; so that this section should be placed higher in the series. The same may also 
I be said with respect to the species of the following section, some of which approach the Arcuata, and 
others the Orhiculata and Trigona. 
