112 | ZOOLOGY. 
general characters of the order, and have seven thoracic and “five or six 
abdominal segments which are quite distinct, the females are misshapen, 
with the segments of the body indistinct. The thorax is narrow in the 
_ male and wide in the female, and the eyes are present in the former and 
absent in the latter. The antenne are more or Jess rudimentary, and the 
feet very short, submarginal, and formed for holding, but not adapted for 
walking and swimming. The male is much smaller than the female. 
Latreille divides the J/sopoda into six families, corresponding to the 
following names: 1, Bopyridw; 2, Cymothoide ; 3, Sphweronide ; 4, 
Idoteide ; 5, Asellide ; 6, Oniscide. : 
fam.1. Bopyride. Bopyrus crangorum is found affixed to the gills, and 
beneath the shell of several large Crustacea, as Palemon and Hippolyte. 
The male is only one fifth or one sixth the size of the female, and is found 
under the abdomen of the latter. When the young leave the egg, they are 
much like those of Cyclops. 
Fam. 2. Cymothoide. Most of these are parasitic upon marine fish, to 
which they affix themselves with the aid of their strongly hooked feet. The 
body is lengthened oval, narrowing towards each end, the head is small, and 
the feet are large and operculiform. The young leave the egg with only 
six pairs of feet, and at this period the abdomen is adapted for swimming. 
Some are sedentary, and others possess the power of walking. The sub- 
families are the Serolinw, Cirolanine, and Nerociline. 
Fam. 3. Spheronide. The genus Spheroma (pl. 78, jig. 21) has the 
thoracic segments nearly alike in form and size, the feet slender, and the 
false feet (except the last pair) received into a cavity beneath the abdomen. 
The species live among submarine plants, and they can roll themselves into 
a ball. Cymadocea (pl. 78, fig. 20) is allied to Spheroma, but it is less 
flexible, and therefore not able to roll itself into a ball. It contains the two 
sub-families, Sphwromine and Ancinine. 
Fam. 4. Idoteide. In this family the four antennz are placed in the 
same line, and the first pair are very small. The body is slender, not much 
thicker in the middle, and truncated or concave posteriorly. The respiratory 
false feet are concealed in an opercular cavity beneath the abdomen. Sub- 
families, Arcturinw and [doteine. 
Fam.5. Asellide. Body elongated and flattened above; the two pairs of 
antennee are setaceous, and arranged in two lines, the first pair small. The 
abdomen is composed of one large scutiform segment without lateral 
swimmerets, and with two terminal stylets. Some of the species are marine, 
and others fluviatile. A species of Asel/ws is common in the fresh waters 
of Europe, and A. communis, Say, Jour. Acad. Nat. Sci. i. 427, is 
abundant in similar localities in the United States; and as it differs from 
the European representative of the genus in having the sides rectilinear, entire, 
and gradually diverging posteriorly, and the posterior segment being the 
widest as well as the largest, and transversely quadrate; we propose to give 
it the generic name of Abacura, from a8a% a table, and ovge the tal. The 
antennee and caudal appendages are as in Asellus. It is half an inch or 
less in length, and may be found walking upon the bottom of springs. 
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