BRANCHIOPODA. 
259 
tlian tlie othei's. It consists of a large, liorny, extremely thin, and 
almost diaphanous scale or plate, which represents the superior tegu- 
ments of the head and thorax united, and forming a large oval con- 
vex shield, angularly notched and dentated at its posterior extremity. 
Its upper surface is divided by a transverse line forming two united 
arcs in two areas, the anterior nearly semilunar, corresponding to the 
head, and the posterior to the thorax. In the middle of the first 
Ave observe three closely approximated simple eyes, or without appa- 
rent facets, the two anterior of which are largest and almost reniform, 
and the posterior much smaller and oval. A duplicature of the ante- 
rior portion of the shell forms a sort of frontal, flattened, semilunar 
shield beneath, which serves as a base to the labrum. The posterior 
area, that which corresponds to the thorax, is carinated throughout 
the middle of its length. This shell is only adherent by its anterior 
extremity, so that looking from this point we can discover the whole 
back of the animal. Each side of the shell, seen from beneath and 
in a strong light, presents a large spot, formed by numerous lines 
describing concentric ovals, which appear to be tubular and filled 
with a red fluid. Directly under the shield or frontal disk, we find the 
antennae and mouth. The former, two in number, ai’e inserted on 
each side of the mandibles, are very short and filiform, and are com- 
posed of two nearly equal joints. The mouth consists of a square, 
projecting labrum ; of two strong, horny, inferiorly inflated mandi- 
bles, compressed and dentated at the extremity and without palpi ; of 
a large and profoundly emarginated ligula ; and of two pairs of foli- 
aceous jaws laid on each other, the superior of which are spinous and 
ciliated along the inner margin, and the inferior almost membranous 
and similar to small false feet ; they are terminated by a slender, 
elongated joint, and are prolonged externally from their base into a 
species of auricle, (oreillette), fiu’nished with an uniarticulated and 
ciliated appendage, which may be considered as a kind of palpus. 
According to Savigny *, the ligula exhibits a ciliated canal, which 
leads directly to the oesophagus. The feet, which amount to about 
one hundred and twenty, insensibly diminish in size, commencing 
from the second pair; they are all strongly compressed, foliaceous, 
and are composed of three joints, exclusive of the two long threads 
at the extremity of the two anterior feet, and the two leaflets at the 
end of the following ones, parts, which, Avhen united, we may con- 
sider as constituting a fourth, forceps-like joint, or one with two 
elongated toes coverted into a sort of antenniform threads. On the 
posterior side of the first joint is inserted a large, branchial, triangu- 
lar membrane; the second also, on the same side, has a red, vesicu- 
lar and oval sac. On the opposite margin of these feet are four trian- 
gular and ciliated leaflets, the superior of which is closely approxi- 
mated to the toes of the forceps, appearing to form a third to the se- 
cond and following feet, as far as the tenth pair. In propoi’tion as 
these organs diminish in size, the leaflets approximate more closely, the 
the forceps is more clearly defined and less pointed, and the first toe 
* M4m. sur les Aniin. sans Verteb., Savig., part I, fasc. I. 
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