ISOPODA. 



433 



The branchiae are in the form of bladders, white in the majority, capable of being puffed op and 

 used in swimming, and covered by two plates or valves of the last segment, laterally adherent to its 

 sides, longitudinal, Inarticulate, opening in the middle in a straight liiie, like a pair of cupboard doors. 

 The tail is formed of three segments, of which the last is the largest, with neither appendages nor 

 lateral swimmerets. All these Crustacea arc marine. 



fiiotea, Fab., have the legs strongly hooked, and all of the same form, and the lateral antenna; are shorter than 

 half tlic body. (OttUeiu Entomon, Linn.) 



Stenotoma, Leach, lias the body linear [and depressed], and the [lateral] antenna; nearly equal to the body in 

 _:h. (Stenotoma lineare, Leach.) 



Arcturut, Latr., is very remarkable in the form of the second and third pairs of legs, which are directed for- 

 ward, and terminated by along hirsute joint, and unarmed or feebly-hooked: the two anterior are applied to 

 the month; the six posterior legs are long, formed for walking, directed backwards, and bifid at the tip. In 



the length of the antenna' and form of the body they approach 8t< notoma, I ba\ ily seen one species (A. tubereu- 



latut), brought from the North Seas in one of the late English expeditious to the Arctic Pole. [This species was 

 published by Sabine under the name of Itlotea Bafjini, but a second species exists in the north of our coast, which 

 I have described in detail, with figures, in the first volume of the Transactions of the Entomological .Society, under 

 the name of Arcturus loiigicornis.] 



The fifth section, Asellota, Latr., is also formed of Isopods, having four very distinct antennae 

 arranged in two lines; they are setaceous, and terminated by a multiarticulate filament, two mandibles, 

 four maxilla', covered in general by a kind of lip formed of the first pair of foot-jaws ; vesicular branchiae 

 disposed in pairs, and covered by two longitudinal, biarticulated, but free plates: the tail is formed of 

 a single segment, and without lateral Bwimmerets, but with two bifid styles, or two vcrv short ap- 

 pendages in the form 'if tub< rcles in the middle of the posterior margin. 



Atetlus, Geoffroy, has two bind styles at the extremity of the body, the eyes distinct, the superior antenna as 

 long as the basal joint of the inferior, ami the hooks at the tips of the legs entire. The only species of this genua 

 U the ldotea aquatica, Fib. (Squilla atettut, DeOeer), which is very abundant in fresh and stagnant water. It 

 crawls slowly, at least, when not alarmed. In the spring it creeps out of the mud in which it had buried itself 

 during the winter. Alter impregnation the female carries her eggs, in great numbers, inclosed in a membranous 

 SBC, placed beneath the breast, ami opening by a longitudinal slit, in order to allow the young ones to escape. 



Oniteoda, Latr. (lanira, Leach) have tie- eyes contiguous, and the hooks of the tarsi bifid at the tips, (lanira 

 maeulota, Leach, found on the coast of England amongst the sea-weeds.) 



Itera, Leach, has only two tubercles at the extremity of the body. (/. albifrons, Leach, also found on the coast 

 of England.) 



The sixth and last section of the order Isopoda, or thcOxisciuES, Latr., have also four antennae, but 

 the intermediate pair is so minute as to be scarcely apparent, and never consists of more than two joints ; 

 the lateral are setaceous. The tail is composed of six segments, with two or four style-like appendages 

 at the posterior margin of the hind segment, and destitute of lateral Bwimmerel : so e Bpecies 



aquatic, but others are terrestrial. In the latter the anterior plates of the under-side of the tail exhibit 

 a row of small boles, through which the air penetrates, and is brought into contact with the respiratory 

 organs, which are inclosed beneath. 



Some of these are marine, and have more than nine joints in the antenna-, (including tie- terminal Bnnuli). 



Tylon, Latr., appears to have the power of roiling itself into a bail; the posterior segment is semicircular, and 



tly tits the incision made by tie preceding; tie- posterior appendages are very minute; the antenna- have only 

 nine | 



lAgia, Fab., have the terminal annuli of the antenna- very numerous, and the body is terminated by two st\ 

 divided at the tip into two branches. 

 The type, Oniii u oeeaniciu, I. inn., is about an inch long, of a gray colour, with two large yellow patches on the 



bark. The lateral antenna- are about hall' the length of the body, tin' terminal filament beinir composed of thirteen 



; he terminal st\;e, an- as long as the tad Itself, it is very common on the coast, clinging to the rock- 

 to the parapets of maritime erections, when it is attempted to be seised it im diately folds up its li 



ami drops. Another species, OnUau hypnormn, Fab., has the terminal division of the anteni •.-band 



the basal part of the anal Styles ar d with a tooth on the inside. 



'li I her (A d, and the lateral antennc have not more than eight Joints, of which the propor- 



irds the extremity gradually diminish, none of them appearing to be divided into annuli. 

 I'll I itr., has the lateral antenna 8-jointed, and exposed at tin- base; the four exterio rappen- 



I ate nearly CqUaL Tie y aie always found in moist situations. iOnitnu tylveitrU, lab. ; U. WUOCCmm, Cm .1 



Oiiisnix, proper, i.iun., have also B-jointed lateral antenn e, but the base is , oncealed, and tie- t» i outer appen- 

 s at the tip of th.- tad are larger than the two internal. The animals of tins and the two following gei 

 are called wood-lice, St. Anthony's bogs, fee. Thej frequent dark and concealed places, such asi 



i i 



