BRANCHIOPODA. 25i) 



than the others. It consists of a large, horny, extremely thin, and 

 almost diaphanous scale or plate, which represents the superior tegu- 

 ments of the head and thorax united, and forming a large oval con- 

 vex shield, angularly notched and dentated at its posterior extremity. 

 Its upper surface is divided hy a transverse line forming two united 

 arcs in two areas, the anterior nearly semilunar, corresponding to the 

 head, and the posterior to the thorax. In the middle of the first 

 we observe three closely approximated simple eyes, or without appa- 

 rent facets, the two anterior of which are largest and almost reniform, 

 and the posterior much smaller and oval. A duplicature of the ante- 

 rior portion of the shell forms a sort of frontal, flattened, semilunar 

 shield beneath, which serves as a base to the labrum. The posterior 

 area, that which corresponds to the thorax, is carinated throughout 

 the middle of its length. This shell is only adherent by its anterior 

 extremity, so tliat looking from this point we can discover the whole 

 back of the animal. Each side of the shell, seen from beneath and 

 in a strong light, presents a large spot, formed by numerous lines 

 describing concentric ovals, which appear to be tubular and filled 

 with a red fluid. Directly under the shield or frontal disk, we find the 

 antennae and mouth. The former, two in number, are inserted on 

 each side of the mandibles, are very short and filiform, and are com- 

 posed of two nearly equal joints. The mouth consists of a square, 

 projecting labrum ; of two strong, horny, inferiorly inflated mandi- 

 bles, compressed and dentated at the extremity and without palpi ; of 

 a large and profoundly emarginated ligula ; and of two pairs of foli- 

 aceous jaws laid on each other, the superior of which are spinous and 

 ciliated along the inner margin, and the inferior almost membranous 

 and similar to small false feet; they are terminated by a slender, 

 elongated joint, and are prolonged externally from their base into a 

 species of auricle, (oreillette), furnished with an uniarticulated and 

 ciliated appendage, which may be considered as a kind of palpus. 

 According to Savigny *, the ligula exhibits a ciliated canal, which 

 leads directly to the oesophagus. The feet, which amount to about 

 one hundred and twenty, insensibly diminish in size, commencing 

 from the second pair; they are all strongly compressed, foliaceous, 

 and are composed of three joints, exclusive of the two long threads 

 at the extremity of the two anterior feet, and the two leaflets at the 

 end of the following ones,* parts, which, when united, we may con- 

 sider as constituting a fourth, forceps-like joint, or one with two 

 elongated toes coverted into a sort of antenniform threads. On the 

 posterior side of the first joint is inserted a large, branchial, triangu- 

 lar membrane ; the second also, on the same side, has a red, vesicu- 

 lar and oval sac. On the opposite margin of these feet are four trian- 

 gular and ciliated leaflets, the superior of which is closely approxi- . 

 mated to the toes of the forceps, appearing to form a third to the se- 

 cond and following feet, as far as the tenth pair. In proportion as 

 these organs diminish in size, the leaflets approximate more closely, the 

 the forceps is more clearly defined and less pointed, and the first toe 



M^m. sur les Anim. saus Verteb., Savig., part I, fasc. I. 



