BRANCIIIOPODA. 441 



vai-yin^ accordiiiff to the length of their oars and the breadth of their shells. According to Strauss, their food con- 

 sists exclusively of minute particles of vegetable substances, which they meet with in the water, and often of 

 confervrc. They constantly refused the animal matter he gave them. It is by the action of their leg's that they pro- 

 duce a current on the water, which brings their food towards the mouth. Tlie hooks at the tip of the tail are 

 used in cleaning the branchiffi. [Mr. Baird has published a detailed account of the anatomy and habits of this 

 genus in the second volume of the Magazhie of Zoolo(ji/ and Bo/ani/.] 



The most common species is B. pidex, {Monoculus pnlex, Linn. ; Pidex aqnaticKs arhorescens, Swammerdam), 

 or the arl)orescent water-flea. It has the seta^ of its oars plumose ; its valves are notched on the lower til'^e, and 

 terminated by a short tail, which is obtuse in the females. 



The last subgenus is Li!nceus,'M\.\\\Qv {Chilodorufi, Leach), distinguished by the oars being shorter than thesliell, 

 and of which the lower part does not form a produced point. All the species have in front of the eye a small 

 black spot, having the appearance of a second [frontal] eye. 



The second section of the BrcmcJiiopoda — that of the Phyllopa — is distinguished from 

 the former by the Tiumbcr of feet, \vhich is at least twenty,* and m some ninch more con- 

 siderable ; their joints, or at least the terminal ones, are flattened, lamellar, or foliaceous, and 

 cibated. The mandibles are destitute of palpi. They have two eyes, (situated in some at 

 the extremity of two moveable peduncles,) and some have also an ocellus ; the antenna;, of which 

 there are generally only two, are small, and not fitted for swimming. These Crustacea compose 

 two principal groups. 



1. Tlie Ceratopthalma, Latr., have at least ten pair of legs, and at the most twenty-two pairs, 

 ^\ithout any vesicular appendages at their base, and of which the anterior are never much longer than 

 the others, nor ramified. The body is inclosed in a shield, formed hke a bivalve shell, or naked, with 

 each of the thoracic divisions bearing a pair of exposed feet. The eyes are sometimes sessile, small, 

 and close together, but more commonly they are situated at the extremity of two movealjle peduncles. 

 Tlie eggs are internal or external, and inclosed in a capsule at the base of the tail. 



In some species the eyes are sessile, immoveable, and the body inclosed in a bivalve shell ; the 

 ovaries are always internal. They form the genus 



Limno.dia of Ad. Brongniart, which so nearly approach the preceding that Hci-mann placed the only species 

 known [to him and Latreille] amongst the Daphnias. The shell is oval, bivalve, and incloses the body, which is 

 long, linear, and inflected in front. Upon the head are placed, 1, two eyes in a transverse direction, and close to- 

 gether ; 2, four anteunffi, two much longer than the others, each composed of an 8-jointed peduncle, and two 

 8-jointed setaceous branches, rather silky, and two others intermediate in situation, small, simple, and dilated at 

 the tips; 3, the mouth, situated beneath, consisting of two mandibles, swollen, curved, and truncate at the 

 inferior extremity, and two foliaceous maxillcc. These parts form together a kind of beak, placed beneath. The 

 body, properly so called, is divided into twenty-three segments, each of which (except the last) bears a pair of 

 branchial feet. All these feet are alike, very compressed, bihd, with the outer division simple, ciliated at the 

 outer edge, and the other 4-jointed, and strongly ciliated on the inner edge. The twelve fore pairs of legs are of 

 the same length, and longer than the others, which diminish gradually in length. The eleventh, twelfth, and 

 thirteenth pairs have at the base a slender filament, bent upwards into the cavity between the back and the shell, 

 serving as the support for the eggs. The ovaries are internal, and situated at the sides of the intestinal canal. 

 The eggs, after being laiil, occupy the dorsal cavity above noticed, and are there attached by means uf small fila- 

 ments adhering to those of the supports. They are at first round and transparent, but afterwards become 

 darker, and irregular in shape. All the individuals observed by Brongniart were provided with them, so that the 

 males remain unknown (if there are individuals of that sex), and are supposed to appear at a ditferent season from 

 the females. The type, Limnad'ta Hennaiini (A. Brongniart, Dap/iina girias, Hermann), has been found in small 

 pools of water in the forest of Fontainebleau. 



[M. Gu^rin has published a monograph upon this genus in his Magasin du Zoologic for 1837, describing three 

 species.] 



[ErJherla, Strauss, (Ci/'i/cus, Audouin,) is a genus closely allied to Lhnnadia, found in the Red Sea. Type, E. 

 D-i/ialacc/isis, Ruppell, in Trans. Mas. Seckenherg, 1837.] 



In the other species of Ceratopthahna, the eyes are placed at the extremities of two long peduncles, 

 formed by the lateral prolongation, hke a nose on each side of the head. The liody is naked, not in- 

 closed in a shield, and annnlated throughout its entire length. The females carry their eggs in an 

 elon-'-ated ca[isnlc, placed at the l)ase of the tail when present, or at the posterior extremity of tlie body 

 and thorax in those which have no tail. 



.-lr^c»'m. Leach, has the body terminated by a tail, the eyes borne at the extremity of very short peduncles; 

 the head confiuent, with an oval thorax, supporting ten pairs of legs, and terminated by a long and pointed taik 



* TliL'ic animals rcpreaeiil in lliis ulass of Crustacea the Myrinpoda in that of the Insecta. 



