412 



CRUSTACEA. 



THE FIRST FAMILY* OF DECAPODA,— 

 Decapoda Brachyura (Kleistagnatha, Fabricius), — 



Has the tail (or post-abdomen) shorter than the thorax, without appendages or swirnmerets 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 



* £i:::: ^^^ N V^Q^>' ,'. ^J^y\Y ^xi^' tne ^ ase f on tne inside], whilst in the female 



it has four pair of double filaments employed 

 in carrying the eggs, and which 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- 

 ber of minute leaflets spread one upon the 

 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 Linnacan 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 



Fiff. 1. — Otrcinus Manas (Common small Edible Crab), upper side and under 

 side of the body, with the limbs truncated. — u, lateral antenna; b, inter- 

 mediate antenna ; c, eye ; d, outer foot jaw ; e,/, g, H, base of the five pairs 

 of legs ; k, tail; /, sternum. 



had long- perplexed Crustaceologists ; and M'Leay, in order to adopt ! 

 his quinarian system to these animals, has divided the Decapoda into 

 five tribes, Tetragonostoma and Trigonostoma (composing the 

 Brachyura), and Anoinura, Sarobranchia, and Caridea (composing 

 the Macruura). — Illustr. Annul us. 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 tlte 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 appeals 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 

 Families Naturelles, in which the tribes here given were introduced 

 but their relative position altered, but in his subsequent fours 

 (TEutomulogie he proposed ano.her arrangcraeut 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.— /. 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 Crustacts, 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, Lithodiadce, 

 and Macropodiadae 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 Canceridse, Portunidae, and Pilnmnids 

 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 Catametopa (Ocypodiadte, Leach), having the carapax quad- 

 rilateral or ovoid, the front transverse and knotted, epistoma very 

 short. 



4. The Oxystoma (Corystidae and Leucosiadae, Leach), with the shell 

 orbicular and arched in front, which is not pointed, epistoma ob- 

 solete. 



