240 CRUSTACEA. 



2. Those — OsTRACODA, Lat. ; Ostrapoda, Straus — whose shell is 

 formed of two }>ioces or valves resembling those of a muscle, united 

 by 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 by a branchial lamina. Their antennae are simple, filiform 

 or setaceous. They never have more than one eye. Their mandi- 

 l)les and superior jaws are furnished Avith a branchial leaf. The ova 

 are placed under the liack. 



.3. The 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 

 hy a kind of shield like a rostrum, exposed. They have two, usually 

 very large, antennpe, resembling arms, divided into two or three 

 brandies directly above the peduncle, which are furnished with 

 threads, always ])roiecting and serving as oars. Their ten feet f are 

 terminated by a digitated or pectinated fin accompanied, the two first 

 excepted, l)y a branchial lamina I- 



Tlieir ova are also placed under the back ; tlieir 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 entij'ely occupied by a larg(; eye. 



The first division of the Lophyropa Branchiopoda — that of the 

 Carcinoida — may be divided into two according to the number of the 

 eyes. 



Some of them have two. 



Here the shell completely invests the thorax ; the eyes are large 

 and very distinct, and the intermediate antennae are terminated by 

 two threads. 



Zoea, Bosc. 



Very large globular eyes completely exposed, and horn-like pro- 

 jections on the thorax. 



Zoea pelarjica, Bosc, Hist, Nat. Crust. U, xv, 3, 4. The 

 body semi-diaphanous ; four antennae inserted under the eyes, 

 the external ones bent into an elbow and bifid ; a kind of long 

 rostrum on the forepart of the thorax and between the eyes, 

 and a long pointed prominence on the posterior part of the 

 back. The feet are very short and liardly 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 sjjinous. It was discovered by 

 Bosc in the Atlantic Ocean. 



* According to Straus, the first pair of feet ; but although these parts ,by serv- 

 ing as oars perform their functions. I nevertheless consider them as analogous to the 

 lateral anteun;e of the superior Crustacea and to the two superior ones of a 

 Cyclops, which here also concur with the feet in producing locomotion. 



f Midler gives eight to the Cytherese ; 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. 



