AMPHIPODA. 427 



1. The Uroptera, Latr., having the head generally large, the antennae often short, and only two 

 in number in some, and the body soft ; all the legs except the fifth pair simple, the anterior short or 

 small, and the tail either furnished at the tip with lateral swimmerets, or terminated by appendages or 

 dilated points, bidentate or forked at the extremity. They reside in the bodies of various Acalepha 

 or Medusce, Linn., and some other zoophytes. 



Some, forming the genus P/H-o«/»«ff, Lat., have only two very short and 2-jointed antennae. The fifth pair of 

 legs is by far the largest, and terminated by a strong didactyle claw. There are six long slender appendages at 

 the extremity of the body, each terminated by two points. There are probably various species, but which have 

 not been described with sufficient care. Type, Cancer sedentarius, Forskal, Faun. Arab., found in the Mediter- 

 ranean, lodged in a membranous, transparent, bell-like bag, probably the body of a Beroe. 



Others have four antennie ; all the legs are single, and the tail is furnished at each side of its extremity with a 

 plate, like a foliaceous swimmeret. 



Hyperia, Latr., having the body thickened in front, the head large and almost entirely occupied by two oblong 

 eyes, somewhat notched at the inner margin, two of the antennae at least half the length of the body, with a ter- 

 minal multiarticulated filament. Type, Cancer monocnloides, Montague, [found on the coast of Devonshire]. 



Phroslne, Risso, difters in having the antennae not longer than the head, and but few-jointed, the terminal fila- 

 ment being conical. 



Dactjilocera, Latr., has the body not thickened in front, the head of moderate size. 



Tkemisto, Guerin, has the third pair of foot-jaws terminated by a small didactyle claw ; the third pair of legs is 

 very much longer than the others. [Many additional subgenera have been recently proposed, belonging to the 

 Uroptera, especially by M. Edwards.] 



2. The second sidjsection, Gammarin^, Latr., have always four antennae, the body covered with 

 a coriaceous elastic tegument, generally compressed and arched ; the posterior extremity of the tail is 

 not furnished with swimmerets, but its appendages are in the form of cylindrical or conical styles. 

 Two at least of the four anterior legs are terminated by claws. 



The vesicular bags in those species in which they have been observed {Gammarus), are situated at 

 the external base of the legs, commencing with the second pair, and accompanied by a small plate. 

 The pectoral scales enclosing the eggs are six in number. 



In the majority the four antennae, although occasionally varying inter se, are applied to the same purposes, and 

 have the same general structure : the inferior never being leg-like. 



lone, Latr., is an anomalous subgenus, founded upon a figure given by Montague, {Linn. Trans., vol. L\. 3, 3, 4.) 

 The body is apparently 15-jointed, the joints being only indicated by lateral incisions ; the four antennie are very 

 short, the external longer than the two others ; the two anterior segments of the body are furnished in the female 

 with two elongated fleshy cirrhi, like oars ; the legs are very short and hooked ; the six tei'minal segments are 

 l)rovided with lateral, fleshy, elongated, fasciculated appendages, simple in the male but branched in the female. 

 Type, Onlscus thoracicus, Montague, found beneath the carapax of Callianassa subterranea, forming a tumour on 

 the sides of its body. Montague kept it alive for several days, having removed it from its native abode. The 

 females are always accompanied by the males, which retain themselves firmly attached to the abdominal ap- 

 pendages of their partners by means of their strong hooks. In regard to its habits, therefore, this animal approaches 

 tlie parasitic Bopyrus. 



All the remaining Amphipods have the segments of the body distinct in their entire breadth, and are destitute 

 in both se.xes of the long oar-Uke appendages found in lone. In some of these the moveable finger of the claw- 

 legs is formed of a single joint. 



Orchestia, Leach, and Talitrns, Leach [comprising British species] have the upper antennae much shorter than 

 the inferior, whilst in the following they are not much shorter, [indeed often much longer. The type of the latter 

 genus is Talitrns locusta, which is very abundant on our shores, burroviing into the sand, and, unlike the majority 

 of the species, seldom entering the water.] In Atyltts, Leach, the upper antenuK are nearly as long as the inferior, 

 the head is produced above into a snout, and none of the legs are cheliferous. Type, A. carinatus, Leach. The 

 t>'pical genus Gammarus, Latr., is distinguished by the isolated character of the superior antennae, having a short 

 branch at the tip of the third joint, and the four fore-legs are in the form of small claws, with the moveable finger 

 folding on the under-side : Cancer pulex is the type. [It is exceedingly abundant in fresh-water brooks, where 

 there is an accumulation of vegetable debris.] Various other genera, as Melita, Leach, Mara, Leach, Amphithoe, 

 Leach, Pherusa, Leach, &c., have been established by Leach and M. Milne Edwards, founded upon variations in 

 their legs and claws. 



Leucotkoe, Leach, has the moveable finger of the two fore-claws biarticulated. The same character also exists 

 in Cerapus, Say, composed of a small species found on the sea-shore of the United States, near Egg harbour, 

 amongst the Seriularicc, and which receives its specific name, C. tubularis, from residing in a small cylindrical 

 tube. [Dr. Templeton has described a small species of Crustacea from JIauritius in the Trans. Entom. Soc, vol. i. 

 p. 189, under the name of Cerapus abditus, which inhabits a little membranous tidie, resembling in texture the 

 papyritious covering of wasps' nests. It is remarkable for wanting feet to the middle segment of its body. Its 

 movements are very singular.] 



