416 



CRUSTACEA. 



The seventh and last section, the Notopoda, is formed of Crabs having the four or two posterior 

 len-s inserted above the plane of the others, and seeming to be dorsal, and directed upwards. In those 

 where they are not terminated by a sharp hook, the animal generally uses them to retain in its hold 

 various marine productions, such as the valves of shells, sea-weeds, &c., with which it covers itself. 

 The tail has seven joints in both sexes ; the majority have the abdomen bent beneath the breast, and 

 the legs terminated by a short hook, and unfitted for swimming. 



Homola, Leacli, have the carapax nearly square ; the aiitennee long ; the ocular peduncles long- ; the claws of 

 the males larg-er than the females, and the posterior pair of legs directed upwards. The outer foot-jaws are long 

 and exposed [as in the Macrura]. The type, H. spinifrons. Leach, is a native of the Mediterranean, and is the 

 Hippocarcbuti of Aldrovandus. 



Dorippe, Fab., has the four hind-legs elevated, as has also Dromia, Fab. 



Di/nomene, Latr., has the carapax of the ordinary form, and the two hind legs alone elevated. 



Ranina, Lam., is a singular genus, ditt'ering from all other Brachyura In having the abdomen extended, [but 

 not furnished at the end with an apparatus for swimming] ; and from the other Notopoda, in having the six 

 intermediate legs dilated and natatorial. The carapax is of a reversed triangular form, the front much toothed. 

 The species are exotic. 



[The Brachyurous Crustacea, here given as a single genus. Cancer, have, from the great number of 

 species of which they consist, their large size, and facility of preservation, owing to their solid envelopes, 

 attracted the attention of many recent authors. The Malacostraca Podopthalma Britannica, of 

 Leach ; the Histoire Naturelle des Crustaces, by Milne Edwards ; the Fauna Japonica, of De Haan ; 

 the Memoirs of Professor Bell, published in the Transactions of the Zoological Society, and by 

 Mr. MacLeay, in Dr. Smith's Illustrations of Southern Africa ; together with Polydore Roux's elegant 

 work upon the Crustacea of the Mediterranean, must be consulted by those who would desire to 

 become acquainted with the singular forms and multitudinous genera established in this tribe of 

 animals.] 



THE SECOND FAMILY OF DECAPODA,— 

 Decapoda Macrura {Exochnata, Fabricius), — 



Is distinguished by having, at the extremity of the tail, on each side, appendages*, ordinarily forming a 

 swimmeret or instrument for swimming, the tail itself being at least as long as the body, extended, 

 exposed, and bent under only towards the posterior extremity. Its under-side generally presents, in 

 both sexes, five pairs of false feet, each terminating in two 

 plates or filaments. The tail is always composed of seven 

 segments. The branchia; are formed of vesicular, bearded 

 and villose pyramids, arranged, in many, either in two rows 

 or in separate bundles. The antennae are generally long and 

 exserted ; the ocular peduncles are mostly short. The external 

 foot-jaws are generally narrow, long, and palpiform, and do 

 not entirely hide the other [internal] parts of the mouth. The carapax is narrow and more elon- 

 gate than in the Brachyura, and ordinarily terminated in front in a point. MM. Audouin and 

 Milne Edwards (to whom we must refer for particulars) have noticed that in the lobster {Astacus 

 marinus, Fab.), in addition to the two large lateral venous canals, there exists a third, lodged in the 

 sternal cavity, in which respect the venous systems of the Macrura and Stomapoda agree. The Ma- 

 crura never [or but in a very few instances] quit the water, and with a very few exceptions they are 

 all marine. 



Adopting the plan of Delper and Gronovius, the Macrura may be considered as forming but a single 

 genus t, Astacus, which may be thus divided : — 



Fig. i.—Geliia stellat:: 



* Tliese appendages are composed of three pieces, namely, a base, 

 (or support to the two others), articulating with the penultimate seg- 

 ment ; the terminal segment generally forming with them a fan-like 

 swimmeret; but in the terminal species the appendages are replaced 

 by filaments. The sub-ahdominal false legs are formed on the same 

 model, and vary in number, there being only three or four small 

 pairs in the Anomala, and wanting in the males {except the antericr 

 pair). In the Hermit Crabs they seem to exist only on one side. But 



in the subsequent subgenera they are constantly larger, and there are 

 five pairs, supporting the eggs ntid being useful in swimmirg. In the 

 section Anomala, the peduncle of the intermediate a tenria is pro- 

 portionably longer, and the two or lour posterior feet smaller, thus 

 approaching the Brachyura. 



t The sections which we have proposed ought rather to form o 

 many genera, based upon those of Fabricius. 



