240 
CRUSTACEA. 
2. Those — OsTRACODA, Lat. ; Ostrapoda, Straus — whose shell is 
formed of two pieces or valves resembling those of a muscle, united 
b}^ a hinge, and closing while the body is quiescent. They have but 
six feet *, neither of which terminates in a digitated fin, nor is accom- 
panied ])y a branchial lamina. Their antennae are simple, filiform 
or setaceous. They never have more than one eye. Their mandi- 
bles and superior jaws are furnished with a branchial leaf. The ova 
are ])laccd under the back. 
3. Tlie last — Cladocera, Lat.; Daphnides, Straus — have but one 
eye, and the shell doubled but without a hinge (Jurine), termi- 
nating posteriorly in a point, and leaving the head, which is covered 
liy a kind of shield like a rostrum, exposed. They have two, usually 
very large, antennae, resembling arms, divided into two or three 
branches directly above the peduncle, which are furnished with 
threads, always ]»rojecting am! serving as oars. Their ten feet j" are 
terminated Ijy a digitated or pectinated fin accompanied, the two first 
excepted, l^y a branchial lamina 
Their ova are also placed under the back ; their body always ter- 
minates posteriorly in the manner of a tail, with two or three threads 
at the end. The anterior extremity of the body is sometimes pro- 
longed into a kind of rostrum, and at others forms a kind of head, 
almost entirely occupied by a large eye. 
The first division of the Lopliyropa Branchiopoda — that of the 
Carcinoida — may be divided into two according to the number of the 
eyes. 
Some of them have two. 
flere the shell completely invests the thorax ; the eyes are large 
and very distinct, and the intermediate antennpe are terminated by 
two threads. 
ZoEA, Bose. 
Very large globular eyes completely exposed, and horn-like pro- 
jections on the thorax. 
Zoea pelaijica, Bose., Hist, Nat. Crust. II, xv, 3, 4. The 
body semi-diaphanous ; four antennoe inserted under the eyes, 
the external ones bent into an elbow and bifid ; a Ivind of long 
rostrum on the forepart of the thorax and between the eyes, 
and a long pointed prominence on the jjosterior part of the 
back. The feet are veny short and hardly visible, the two last 
excepted, which arc elongated or terminate in a fin. The tail 
is as long as the thorax, curved, and formed of five joints, the last 
being large, crescent-shaped and spinous. It was discovered by 
Bose in the Atlantic Ocean. 
* According to Straus, the first pair of feet ; hut although these parts ^by serv- 
ing as oars perform their functions. I nevertheless consider them as analogous to the 
hvteral antennee of the superior Crustacea and to the two superior ones of a 
Cyclops, which here also concur with the feet in producing locomotion. 
't' Muller gives eight to the Cytherece ; reasoning from analogy, we may presume 
that he was mistaken. 
:{: This character applies especially to Daphnia, the most numerous subgenus of 
this division, and by analogy, to Polyphemus and Lynceus. 
