HRANCUIOPODA. 259 



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

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

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

 vex .shield, singularly notched and dentated at : :i or extremity. 

 Itr, upper Mitlar.- U divided by a transverse line forming two united 



in t\\-D areas, tin anterior nearly semilunar, corresponding to the 

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

 \\e observe three closely approximated simple eyes, or without appa- 

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

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

 rior ]jortioii of the shell forms a sort of frontal, flattened, semilunar 

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

 that which corresponds to the thorax, iscarinated throughout 

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

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

 h u-k 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 inandi- 

 e.ompressed and dentated at the extremity and without palpi ; of 

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

 is jau > laid on each other, the superior of which are spinous and 

 eiliated 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 

 1 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 i-oinj rased 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- 

 >ider 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 m> inl'r.ine ; 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 



e organs diminish in .si/.-, the leaflets approximate more closely, the 

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



M*m. ur Ics Anim. tn Verteb., Savig., part I, fasc. 



