THE CRETACEOUS FORMATION. 5 



others, but are bent backwards and upwards for the support of the ovaries. In one 

 genus, Cypridina, there are two separate eyes, one on each side of the median Hne of 

 the body, but in general the eye is single, that is, coalesced ; it is situated near the 

 back and rather anteriorly. 



The Cypris, Miiller/ is the best known genus of this section. It is found only in 

 fresh water ; and many species may be readily taken among the weeds of our brooks 

 and ponds. It has two pairs of antennas, both plumose, and two pairs of feet. It is 

 very active, swimming rapidly, chiefly by means of its antennae, or creeping more 

 leisurely on the submerged water-plants. 



The Candona, Baird,^ inhabits fresh and brackish waters, and is of a larger size 

 than the foregoing. It has two pairs of antennae, the superior pair only being furnished 

 with long setae, and two pairs of feet. Having the inferior antennae hooked merely 

 and not plumed it is unable to swim ; its movements are sluggish, and it lives chiefly 

 on or beneath the surface of the mud. This genus, previous to Dr. Baird's researches 

 on the natural history of the British Entomostraca, was confounded with the foregoing. 



Both of these genera occur in a fossil state, the latter in the Pliocene fresh-water 

 deposit at Grays, Essex ; the former in the Carboniferous, Wealden,^ and Tertiary 

 formations. 



The Cythere, Miiller,* has three pairs of feet, all protruded from the shell; the 

 antennae are simple ; and the pediform antennae, instead of a bundle of setae, as in 

 Cypris, possess one stout, articulated filament. This animal is marine,^ probably 

 altogether littoral, creeping at the bottom and among sea-weed. 



The fossil remains of Cythere and its subgenera are very abundant, especially in the 

 Lias and the various members of the Oolitic, the Cretaceous, and the Tertiary forma- 

 tions. They occur also in the Carboniferous and Magnesian limestones, and in the 

 Silurian rocks. 



The genus Cypridina, Milne Edwards,® is marine, and has been taken in deep 

 water only. It is furnished with two eyes, two pairs of antennae, one pair of natatory 

 feet, and a pair of oviferous feet. 



Three fossil species from the Carboniferous rocks of Belgium have been figured 

 and described by M. de Koninck,'^ one species from the Carboniferous limestone of 



^ Entom. pp. 36, 54 et seq. Baird, Mag. Zool. Bot., vol. i, pp. 518 et seq. ; and Ann. Mag. Nat. 

 Hist., vol. xvii, p. 413. 



2 Trans. Benv. Nat. His. Club, vol. ii, p. 152, 1845. Ann. Mag. Nat. Hist., vol. xvii, p. 414. 



* There is, however, reason to believe that some, if not all, of the species found fossil in the Wealden 

 are more nearly allied to the genus Candona than to Cypris. 



* Entom. pp. 36 et seq., 63 et seq. Baird, Mag. Zool. Bot., vol. ii, pp. 138 et seq.; and Ann. 

 Mag. Nat. Hist., vol. xvii, p. 414. 



^ Dr. Baird informs me that a fresh-water species has lately been discovered. 



^ Hist. nat. Crust., tome iii, p. 407. Hist. nat. Auim. s. Vert., sec. edit., torn, v, p. 1/8. Baird, 

 Ann. Mag. Nat. Hist., second series, vol. i, pp. 21 et seq. 



'' Mem. Crust, foss. Belgique, 1841. Descript. Anim. foss. terrain Carbonif. Belgique, 1842. 



