428 



CRUSTACEA. 



-Corophium longicorne ; 

 the tail. 



terminal segment of 



Podocerus, Leach, and Iassa, Leach, have the inferior antenna; greatly elongated in the form, and occasionally 

 assuming the functions of legs and organs of prehension ; their second legs are terminated by a large claw. 



Corophium, Latr., has similar lower antennae, but none of the legs are cheliferous. The type is Cancer 

 grossipes, Linn., Gammarus longicornis,¥ab., Oniscus rolutator, Pal., and which is named Pernys on the coast of 

 La Rochelle, living in burrows, which it forms in the sand, covered by hurdles, called bouchots by the in- 

 habitants. The animal only makes its appearance at the beginning of May. It keeps up a continual war 

 with the Nereids, Amphinomae, ArenicoU-e, and other marine annelids which take up their abode in the 

 same place. Nothing is more curious than to observe these creatures at the rising of the tide assembled in 

 myriads, moving about in all directions, beating the mud with their arm-like antenna:, and diluting it in order to 

 discover their prey. If they discover any of these annelidae, often 

 ten or even twenty times larger than themselves, they unite 

 together to attack and devour it. The carnage never ceases 

 until the mud has been turned over and examined. They 

 also attack fishes, mollusca, and dead bodies on the shore. 

 They mount upon the hurdles which contain muscles, as well as 

 upon the latter, and the fishermen pretend that they cut the 

 threads which retain the muscles, in order to cause the latter to 

 fall, so that they may be the more readily devoured. They appear 

 to breed throughout the season, as the females are found carrying eggs at different times : shore-birds and many 

 kinds of fishes devour them. 



The second of the sections of the order Amphipoda, or the Heteropa, Lat., is composed of those which 

 have fourteen legs, the four posterior at least being unarmed at the tip, and fit only for swimming,* 

 and forms two subgenera. 



Pterygoura, Latr., has the thorax divided into numerous segments, four antennae, with long hairs ; all the 

 legs natatorial, and of which the posterior are large and pennated. [Type, Oniscus arenarius, Slabber.] 



Apseudes, Leach (Eupheub, Risso), has the thorax divided into numerous segments, the fore pair of legs 

 terminated by a large claw, the second pair of legs with the terminal joints very broad and toothed [whence the 

 specific name of the type, A. talpa, Leach, Montague, from its analogy with the Mole] ; the other legs are single, 

 the body is long and narrow, terminated by two long threads. 



Rhaa, Edwards, diners from the preceding in having the superior antenna; thicker, longer, and bifid. 



The third and last section of the order Amphipoda, or the Decempoda, Lat., consists of species 

 having only ten feet. 



Typhis, Risso, has only two antennae ; the head is large, with prominent eyes ; each pair of legs is attached to 

 a distinct segment ; the four anterior are terminated by a didactyle claw. On each side of the thorax are two 

 moveable plates, forming two valves, beneath which, when at rest, the animal shuts its legs and tail, giving it the 

 appearance of a ball. Type, Typhis ovoides, Risso. 



Anceus, Risso, Gnathia, Leach, has the thorax divided into the same number of segments as there are pairs of 

 legs, which are simple and monodactyle. They have four antennae ; the head is large and square, and furnished 

 in front with two great projections, like mandibles. Type, Cancer maaillaris, Montague, Trans. Linn. Soc, 

 vol. vii. pi. 6, f. 2, — found on the Devonshire coast. 



Praniza, Leach, has four antenna; like the last, but the thorax from above presents only three segments, of 

 which the two anterior are very short, and the third very large and oval, having the three posterior pairs of legs 

 attached to it. The legs simple, the head triangular, and the tail furnished at the sides of the extremity with a 

 swimmeret. [I have investigated the structure of this curious genus very minutely, and published the result 

 thereof in the Annales des Scietices Naturelles, vol. xxvii.] 



To this order also appear to belong various other genera, established by Savigny, Rafinesque, and 

 Say, but of which the characters have not been hitherto given with sufficient decision ; and even of 

 those cited above some require a re -examination. 



* M. Milne Edwards has collected many valuable and detailed observations on many of these Crustacea, 

 which will serve to clear up much of this obscurity. I am not able to speak with precision also of the 

 genus Ergina of Risso. From the number of legs it appears to belong to the last section of the Amphi- 

 poda, but the manner in which they terminate, and the number of the segments of the body, range them 

 amongst the Isopods. 



[Since the publication of the second edition of this work, the Amphipoda have received a consider- 

 able share of attention. M. Milne Edwards, in the Annales des Sciences Naturelles for 1830, published 

 a revision of the order, dividing it into two principal groups, (removing the genera Rhoea and Tanais to 



• This and the following section formed, in the first edition of this to us to approximate them to the Amphipoda, and not theIs>poda. 

 work, the second of the Isopodous order, that of Phvtibranches But 1 Nevertheless, these animals, of which the number is but very small, 

 not only have we perceived mandibular palpi in some of these Crus 1 have been very imperfectly studied. 



tacea, but also the form of the subabdoininal appendages has appeared ] 



