DECAPODA. 412 1 



is always prolonged into a point, often forming a sharp-pointed plate, very much compressed, and 

 tootlied on both edges. The antennae are always advanced ; the lateral ones generally very long, and 

 in the form of a very slender thread : the intermediate antenna, in the majority, are terminated ])y 

 three filaments. The eyes closely approach each other. The outer foot-jaws, longer than ordinary, 

 resemble palpi or antennae. One of the two fore pair of legs is often folded back, or doubled. The seg- 

 ments of the tail are dilated laterally. The outer plate of the terminal swimmeret is always divided la 

 two by a suture, as in the terminal species of the preceding section. The middle piece, or the seventh 

 and last segment of the tail, is long, narrowed towards the tip, and is armed above with rows of small 

 spines. The false legs, of which there are five pairs, are long and foliaceous. These Crustacea are much 

 eaten in different parts of the world, and some species are salted for keeping.* 



Those wliicli have the three anterior pairs of legs didactyle, the length gradually increasing, so that the third 

 pair is the largest, compose the genera Peiicciis, Fabr., (having no annular divisions in the joints of the legs, and 

 composed of numerous species, one of which, the Caramote (P. sulcatus, Oliv.), is very common in the Mediter- 

 ranean, and is a great object of commerce, being salted for exportation to the Levant, and of which the English 

 species (P. trisulcatus. Leach) is considered by Latreille to be a local variety), — and Htcnopus, Fabr., having the two 

 penultimate joints of the four posterior legs with annular divisions. 



The remaining species have not more than the two anterior pairs of legs didactyle, and the intermediate antenna 

 terminated by three filaments. 



Al>)a, Leach, formed of a single North American species, A.scabra, is anomalous in the form of its four claws, 

 which are small, and split to the base with long tenninal pencils of hair, the preceding joint being crescent-shaped. 



The others have the claws of the ordinary didactyle form. These, with the exception of the tenninal genus, have 

 the legs more or less robust, but not filiform, without any appendage at the base. The body is neither very soft, 

 nor very much elongated. 



Crangon, Fabr., has the fixed finger or index of the two anterior and largest claws reduced to a small tooth, the 

 moveable finger being hook-shaped. The superior or intermediate antennae have only two terminal filaments ; the 

 second legs are folded, and more or less distinctly didactyle at the tips ; none of the joints are annulated ; the 

 rostrum is very short. Crangon vulgaris, Fabr., the Common Shrimp, is the type of this genus. It does not 

 exceed two inches in length, and is of a pale glaucous green colour, dotted with grey. It is caught throughout 

 the year with the assistance of circular nets. Its flesh is debcate. 



Pontophilus, Leach (Egeon, Risso), does not generically ditt'er from Crangoit. 



Processa, Leach {Nika, Risso), has one of the fore-legs terminated in a point, and the othrr didactyle. The 

 second pair of legs are of unequal length, one being very long, with the two joints preceding the claw annulaled. 

 IV. edulis, Risso, found at the nioutli of the Rhone. 



Ilymenocera, Latr., ditters in the proportions and form of the legs. 



To these succeed a number of genera in which the legs and claws do not present any anomalous structure, and 



in which the superior or intermediate antennaj have only two terminal filaments, including the genus Hippolyte, 



Leach, comprising several British species of shrimps, and in which the four fore-legs 



are terminated by a didactyle claw, the second pair being longer than the first ; and 



Pamlalus, Leach, comprising another British species (P. aiiiiii/iconiix, Leach), in 



"^^^Tv^^^^'*''^^"^?^ which the fore-legs are [very small and] simple, or scarcely bifid ; the two following 



ri:yj ] long, of unequal length, with the two joints preceding the claw annulated. 



The Trawn is the type of the genus Pahemon, which difl'ers from the last group 



rig. 7 — HipiJolyte vanaiis. . i , .-i .. ». , 



of genera in having the upper antennai termmated by three hlaments. It has 

 the two anterior pairs of legs didactyle, the smaller pair being folded ; and the carpus is not aiticulated. The 

 rostrum is very long [and spined]. Some of the exotic species acquire a very large size, with the second pair of 

 legs very long. The flesh of the common species is more esteemed than that of the Shrimp. According to M. 

 de Brebisson (Cat. Melh. Crust. Depart, du Calvados), they are caught in the same manner as Shrimps, hut only 

 in summer. They sw im well, especially when alarmed, and in difierent directions. They frequent the coast. The 

 lithographic stone of I'appenheim and Sohlnofe;i often contains the remains of a fossil species, which Desinarest 

 names Pahemon spinipes. Another fossil si)ecies, but of a much larger size, has been found in England. The 

 species ordinarily sold in the fish-shops is the Paldumon serratus. It is generally three or four inches long, and of 

 a pale red colour, which is brightest in the antenna;, and especially in the swimmeret of the tail. Its frontal spine 

 extends beyond the peduncle of the ndddle antenna; : it is curved upwards at the tip, with seven or eight spines 

 above, and five beneath. One of the sides of the body is often distended, which is caused by a parasite of the 

 genus Bopyrus beneath the carapax, aftixed to the branchia;. Pahaiwn squilla, Linn., is another but smaller 



• [The graclual develiipciuciit of s,.veral species of Cnriilus (P.hc- 

 lonidEc) has been rceciilly deseribeJ by Dr. ,1. V. Thompson in J.imc- 

 oil's Edinb. Phil. Juurn., Oct. 18:i6, and by Captain Ducane in the 

 Innah uf Nut. Hist., Nov. 183S. On first burstinR from the cgif, the 

 .til is terminated by a spatulatcd plate, destitute of lateral as well :ls 

 ubabdoniinal appendages; the rostrum is produced into a simple 

 the lateral antennic exhibit only the larjje scale ; and only tivo 



and ridye of the carapax spined; tlie five pairs of legs extttuled to 

 their full size, but still bifid ; and the subabduminal appendages ami 

 the swiinnierets (jraduullv dei'eloped. These observations are as- 

 serted, byM'Lcayand others, to aflford a complete eotitiriiiatinn of 

 the correctness of Thompson's assenions that Zoea is the larva of the 

 common Crab, and that all the Crustacea uiideruo lran>fornialioiis,— 

 these gentlemen overlooking the fact that Zoea is a Decapod animal, 



of the legs are of the ordinary length, and these are bifid, as in the . not furnished with bifid legs, but having the two pairs of enter fooi- 

 Rchizopods: Oic other legs are very minuir, and incurved. In the jaws immensely dpvelo|ied, but of the ordinary Mnciuuious tunslruc- 

 eourse of several moulUngs, the anteiiiiic ate kiiglhcncd ; the ro:.lrum I lion, as ate the iulcinal puts ol its inoulh] 



