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Show 84 CRUSTACEA. angular dilatation, and their posterior extremity exhibits two teeth( 1 ). In ALIMA, Leach, The fir·st joint of the ocular pedicJes is slender, cylindrical, and much longer than the following one; the body is narrower and more elongated than that of an Erichthus; the lateral borders of the shield are nearly straight or are but slightly dilated; thet·e is a slight longitudinal cat·ina ou its middle, and each of its angles forms a spine, the two posteriot· of which arc the largest(2). FAMILY II. BIPELTATA. In this family we find the shell divided into two shields, the anterior of which, very large and more or less .oval, forms the head, and the posterior, corresponding to the thorax, ~ransverse and angular in its circumference, supports the footJaws and feet. These latter, with the exeeption at most of the two posterior and two last foot-jaws, are slender and fiJiform, usually very long and accompanied by a lateral, ciliated appendage. The other four foot-jaws are very small and conical. The base of the lateral antennre exhibits no scale· the intermediaries are terminated by two threads. The ocu-' lar pedicles are long. The body is much :flattened, membran~ us, and ?iaphanous; the abdomen small and its posterior fin Without spmes. It comprises but a single genus, the PHYLLOSOMA, Leach, Of which all the species inhabit the Atlantic Ocean and Oriental seas(3). (1) Ericltthus vitreus, Lat. See art. Squille, Atl. d'Hist. Nat. of the Encyclop. Method., pl. cccliv; and Desmar. Consid., XLIV, 2, 3. (2) .lllima ltyalina, Lat., Encyclop. Method., art. Squille, and Ibid. Atl. d'Hist. Nat., CCCLIV, 8; Desmar., Consid., XLIV, 1. (3) See Encyclop. Method., and Nouv. Diet. d'IIist. Nat., Ed. II, article Phyl· losorne,· u~so the work of Dcsmarcst on the Crustacea and the Zoology of the Voy. de Fre~cmet. As respects their nervous system, the Phyllosomre seem to be intermedtate between the p.receding and subsequent Crustacea. See Audouin and ~dwards, op. cit. CRUSTACEA. 85 MALACOSTRACA. b. Eyes sessile and immovable. The Branchiopoda are the only Crustacea of. ":hich we shall henceforward have occasion to speak, that exhibit eyes place.d edicles. But independently of the fact that these pedt-on p . . 1 . . h 1 are neither articulated nor lodged m spec1a cavities, t e ces . d f Branchiopoda have no shell and are otherwise remove rom the preceding Crustacea by various cha~acters. All the M~lacostraca of this division are also deprived of a shell; ~heir b dy from the head downwards, is composed of a smte of 0 articu' lations of which each of the fi rst seven I.S f urm.s h e d with a pair df feet, the following and last ones, s~ven at most, forming a sort of tail terminated by fins or styhfor~ appendages. The head presents four antennre, the two Intermediate superior, two eyes, and a mouth composed o~ two mandibles, a tongue, two pairs of jaws, and a sort of l~p formed by two foot-jaws that correspond to the two superior ones of the Decapoda ; here, as in the Stomapoda, the :agr~~ no longer exists. The four last foot-jaws a~e t~ans orme mto feet, sometimes simple and at others constituting a claw, but almost always with a single toe or hook. . According to the observations of Messrs ~udoUin and Edwards, the two ganglionary cords of the spmal marrow are perfectly symmetrical and distinct througho~t t~e whole of their length, and from those of the Baron Cuvier It would appear that the Onisci are only remov~d fr~m ~hem because these cords do not present the same uniformity In all the segments of the body, and because there are some ganglions less(l ). Thus, according to them, the nervous system of the Crustacea is the simplest of all; in the Cymothore and ldotere the two ganglionary chains are no longer distinct, and those (1) See ONI~cus. |