ISOPODA. 
231 
six segments, the last of which fs large and suborbicular. Such is 
the 
Limnoria, Leach, 
The only living species known is the Limnoria terebrans, 
Leach, Edinb. Encyclop., VII, p. 433 ; Desmar., Consid., p, 
312, Although scarcely above two lines in length, its habits 
and fecundity render it highly noxious. It perforates the tim- 
bers of ships in various directions and with alarming rapidity. 
Wlien taken in the hand it rolls itself into a ball. It is found 
in various parts of the British seasr 
The figure and description of a small fossil crustaceous ani- 
mal has been sent to Count Dejean by Professor Germar, which 
seems to ns to belong to this subgenus *. 
The third section — Sph,eromides, Lat. — exhibits four very dis- 
tinct, short, setaceous or conical antennae, and a single genus — An- 
thura — excepted, always terminated by a stem divided into several 
small joints ; the inferior, always the longest, are inserted beneath 
the under part of the fii’st joint of the superior which is broad and 
thick. The arrangement of the mouth is as usual. The branchiae 
are vesicular or soft, exposed, and arranged longitudinally in pairs. 
But two complete and moveable segments are observed in the tail, 
the first, however, frequently presents impressed and transverse 
lines indicating vestiges of others ; on each side of its posterior ex- 
tremity is a fin terminated by two leaflets, of which the inferior alone 
is moveable; the sujierior f is formed by an internal j^rolongation 
of the common stem. The branchial appendages are curved in- 
wards: the inner side of the first are accompanied, in the male, by a 
small linear and elongated projection. The anterior part of the 
head situated beneath the antennae is triangular, or has the figure of 
a heart reversed. 
Some have an oval or oblong body, usually assuming, when con- 
tracted, the form of a ball ; the antennae terminated by a pluri-articu- 
lated stem, and the inferior, at least, visibly longer than the head. 
The lateral and posterior fins are composed of a peduncle and two 
laminae, forming with the last segment a common fin, shaped like a 
fan. 
In these, the impressed and transverse lines of the anterior seg- 
ment of the tail, which is always shorter than the next or last one, 
do not extend to the lateral margin. The first joint of the siqjerior 
antennae has the form of a triangular palette. 
The head, viewed from above, forms a transverse square. The 
leaflets of the fins arc much flattened, and the intermediate piece or 
the last segment is widened and rounded laterally. 
* The Oniscus prtecjustator, figured in Parkinson, is allied to this species, or at 
least, appears to belong to the same section. 
t It folds over the posterior edge of the last segment, and in several, such as the 
Zuzara:, and Nasee, Leach, like an arch. 
