194 PITH OF THE PERIODICALS. 



posterior extremity. Feet ten, more or less divided, and fur- 

 nished at their extremities with bristles. Tail short, folded 

 below the body, and terminated by two conical or setaceous 

 appendages. Eggs interior, until the moment of deposition 

 in the water ; ovary lateral, in a dorsal cavity between the 

 body and testaceous covering. Genera, Polyphemus, Dajj/i- 

 niu, Lijnccus. 



Order. — Ostrapoda. 



Covering forming an oval bivalve shell laterally compressed, 

 bent and dorsally inflated, and almost straight, or a little 

 notched on the opposite side. Before the hinge in the median 

 line the eye appears like a large black spot. The antennae 

 inserted immediately below are setaceous, shorter than the body, 

 composed of seven or eight articulations, of which the last are 

 the shortest, and terminated by a fascicle of bristles, which assist 

 the creature in swimming, and which, according to Jurine, the 

 animal develops in different degi'ees, as it desires to move itself 

 more or less rapidly. The mouth is composed of a carinated 

 labrum and two dentate mandibles, each bearing a triarticulate 

 palpus. The feet are six in number, of which the anterior 

 (the strongest pair), are directed forwards, terminated by two 

 joints, furnished with stiff bristles, or long hooks, and situated 

 below the antennae ; the other feet are without these bristles ; 

 the second are first thrown back, bent and terminated in a 

 long and strong hook ; the last pair are not seen outwardly ; 

 they are raised and placed by the sides of the body, they 

 support the ovaries, and terminate in two small hooks. Ge- 

 nera, Cypris, Cytherea. 



Order. — Phyllopoda. 



The Phyllopoda have a body sometimes naked, at others 

 defended by a case which envelops them, in the manner of a 

 bivalve shell, or else covering them above, in the form of a 

 semi-oval buckler, is divided into a great number of small 

 segments, each of which, with the exception of the last, bear a 

 pair of foliaceous feet : it is often terminated by a tail, having 

 at its extremity two threads or appendages adapted for swim- 

 ming. The head has two eyes, and sometimes even three ; four 

 or two antenna?, a labrum, two mandibles ; four or tvvomaxillse 

 and a tonijuc. 



