412 CRUSTACEA. 
THE FIRST FAMILY* OF DECAPOD A,— 
Dec APOD A Brachyura {Kleistagnatha, Fabricius), — 
Has the tail (or post-abdomen) shorter than the thorax, without appendages or swimmerets at its 
extremity, and in a state of rest folded beneath the breast, and lodged in a sternal cavity. 
It is triangular in the males, but rounded 
and swollen in the femalesf, and is furnished 
in the former with four or two appendages at 
the base [on the inside], whilst in the female 
it has four pair of double filaments employed 
in earrying the eggs, and whieh are analogous 
to the swimming sub-abdominal appendages of 
the Macrura. The antennae are small ; the 
intermediate pair, generally lodged in a cavity 
beneath the fore-margin of the carapax, are 
terminated by two very short [articulated] 
filaments. The peduncles of the eyes are 
larger than in the Macrura. The first pair of 
legs is terminated by a claw. The branchiae 
are arranged in a single row in the form of 
pyramidal plates, composed of a great num- 
mediate antenna ; c, eye ; rf, outer foot jaw j e,/, g-, A, base of the five pairs ^6^ of minUte leaflets Spread One UpOn the 
of legs; k, tail; sternum. , i , 
Other : the foot-jaws are ordinarily shorter 
and broader than in the Decapods, the outer pair forming a kind of labium. 
This family may be regarded as constituting the single genus 
Cancer, — 
Comprising the numerous species of crabs [and consisting of a portion only of the Linnsean genus 
Cancer, divisible into seven sections and a great number of minor divisions, regarded by recent authors 
as genera]. Of these the majority have the legs attached at the sides of the breast, and always ex- 
posed. The species thus characterized constitute the first five sections, Pinnipedes, Arcuata, Quadri- 
latera, Orbiculata, and Trigona.J 
had long perplexed Crustaceologists ; and M'Leay, in order to adopt 1 
his quinarian system to these animals, has divided the Decapoda into 
five tribes, Tetragonostoma and Trigonostoma (composing the 
Brachyura) , and Anomura, Sarobranchia, and Caridea (composing 
the Macroura). — Illustr. Annulos. of South Africa, No. 3.] 
* The groups thus indicated are founded upon a general survey of 
important anatomical characters, and generally correspond with the 
Linnsean genera, and sometimes also to those of the earlier works of 
Fabricius. These families are here of greater extent than in my 
other writings ; but if we regard these as primary ordinal divisions, 
and the groups here called tribes as families, the arrangement will be 
found essentially identical. In the same manner the subgenera here 
indicated ought, in a more detailed arrangement, to be regarded as 
genera, and thus, although the Decapoda are here only divided into 
two genera, it would be correct, in order to bring the system to the 
level of our present knowledge, and in order to diminish the vast 
number of sub-genera, to convert the sections into tribes or genera, 
which might then be divided into subgenera. 
t The apparent number of segments is generally seven, varying 
occasionally in the sexes of the same species, in which case the 
females have the least number. Dr. Leach made great use of this 
character, but it appears to me to be too unimportant. 
t [Latreille regarded this arrangement of the Crabs here given as 
artificial in many respects, and he had modified it not only in his 
Pamilles Naturelles, in which the tribes here given were introduced 
but their relative position altered, but in his subsequent Cours 
d’ Entomologie he proposed another arrangement of the order, as 
follows : — 
Section 1. Homocheles, claws of equal size in both sexes. 
Division 1. All the feet attached to the body in the same line. 
Tribes.— 1. Quadrilatera, 2. Arcuata, 3. Pinnipedes, 4. Christi- 
mani, 5. Cryptopoda. 
Division 2. With the two or four posterior legs dorsal. 
Tribe. — 6. Notopoda. 
Section 2. Heterocheles, claws of the males larger than those of the 
females. 
Division 1. All the legs in the same line. 
Tribes. — 7- Orbiculata, 8. Trigona. 
Division 2. Hind pairs of legs very small, and either dorsal or 
abortive. 
Tribe.-~9. Hypopthalma. 
Dr. Leach, as above mentioned, adopted the number of abdominal 
segments, and was consequently led to distribute this order into still 
more numerous families. Milne Edwards, however, in his Hist. Nat. 
des Crustacis, now in course of publication, has, from anatomical 
considerations, considered it more natural to separate the Brachyura 
into only four great families. 
1. The Oxyrhycha (Trigona, Latr. or the families Maiadae, Lithodiadse, 
and Macropodiad® of Leach), consisting of the sea spiders or thorn- 
backed crabs, the legs being long, the carapax narrowed into a point 
in front, the epistoma very large and nearly square. (Three tribes, 
Macropodiens, Maiens, and Parthenopiens). 
2. The Cyclometopa (or the Cancerid®, Portunid®, and Pilumnid® 
of Leach)! carapax very large, arched in front, narrowed behind, legs 
moderately long, epistoma very short, transverse. (Two tribes, 
1. Canceriens, composed of three sub-tribes, Cryptopoda, Arcuata, 
and Quadrilatera; and, 2. Portuniens or Pinnipedes). 
3. The Cataraetopa (Ocypodiad®, Leach), having the carapax quad- 
rilateral or ovoid, the front transverse and knotted, epistoma very 
short. 
4. The Oxystoma (Corystid® and Leucosiad®, Leach), with the shell 
orbicular and arched in front, which is not pointed, epistoma ob- 
solete. 
■t 
