POLYPHEMUS. CRUSTACEA. 185 



ly conical, of six segments, of which the first is the largest, and 

 the last terminated by a bifid tail. T 5 ^ of a line long. Desm. 

 Crust, pi. 53, fig. 6. 



C. castor, Desm. (M. cceruleus, Fab.) Body elongated, slightly 

 gibbous, of six segments ; tail short, of six segments ; posterior 

 antennae short, bifid. 1^ line long Desm. Crust, pi. 53, fig. 5. 



FAMILY II. OSTRACODA. 



Shell either folded in two, or in the form of two valves united 

 by a hinge, and inclosing the body. 



Gen. 2. POLYPHEMUS, Mull. Monoculus, Lin. 

 Head separated from the body by a strangulation ; one eye ; 

 shell plicated in two ; no hinge ; body short, globular ; two 

 small cirri, each of a single joint, below the eye ; two large 

 antennae in the form of arms ; tail slender, elevated over the 

 back, and bifurcated ; eight apparent feet. 



P. stagnorum, Muller, (M. pediculus, Lin.) Inhabits the water of 

 ponds and marshes, in great numbers, and swims on its back. 

 Desm. Crust, pi. 54, fig. 1-5. 



Gen. 3. DAPHNIA, Muller. Monoculus, Lin. 

 Body elongated, compressed ; shell bivalve, transparent, open- 

 ing under the belly with a hinge on the back ; head distinct 

 from the body, in the form of an inflected rostrum ; one eye, 

 inclosing about twenty small areolae ; two small cirri or an- 

 tennae at the extremity of the rostrum below ; abdomen of 

 eight segments ; feet ten, complicated. 



The animals of this genus are abundant in stagnant waters, at some periods so much 

 so as to colour the water. One species, of which the colour is red, has sometimes 

 giyen rise to the popular opinion that the water in which they abounded was converted 

 into blood. 



D. pulex, Lat. Body red in spring, rose-coloured in summer, and 

 greenish-white at other seasons. 1 line long. This species has 

 been the subject of many observations by Swammerdam, Lewen- 

 hoeck, De Geer, and Jurine. Inhabits stagnant waters in Europe. 

 --Desm. Crust, pi. 54, fig. 1, &c. 



Gen. 4. LYNCEUS, Mull. Monoculus, Fab. 



Body rounded, compressed, inclosed in a shell, of which a pro- 

 jecting line on the back represents the hinge ; head more or 

 less separated from the body by a notch of the shell above ; 

 two black points, one behind the other, considered as eyes ; 

 two antennae in the form of long bifid arms ; ten feet ; tail 

 pointed, generally folded below and inclosed in the shell. 



L. roseus, Desm. One of the smallest of the order, about y \ of a 

 line ; rose-coloured, with the intestines yellowish brown, and the 

 ova contained in a dorsal matrix ; a large filament at the upper 

 branch of the antennae. Desm. Crust, pi. 54, fig. 8, 9. 



