OCR Text |
Show 64 CRUSTACEA. immense numbers that the Ocean seemed to be of one blood-red colour. The JEglea, Id., is only distinguished from the preceding genus, and f1·om Galathea, by the dentation of the mandibles, by the second joint of the external foot-jaws being shot·ter than the first, and by the surface of the body being generally smooth( 1 ). That which Risso first named CALYPso, and subsequently JANtRA, in the opinion of Dcsmarest,-Considcr., p. 192, docs not differ from Galathea. PoacELLANA, Lam. The Porcellanre f0rm a singulat· exception among the Macroura, ,vith respect to their tail, which is doubled undu as in the Bt·ach. yura. They are othcnvise removed ft·om the Galatbcc:c by the more abbreviated, suborbiculn.r, or almost square form of theit· thorax; by the mediate antcnnc:c, which are sunk in theit· fossulre, by theit· tri. angular forceps; and finally, by the internal dilatation of the ·infcrior joints of theit· external foot-jaws. Their body is very flat. They arc small, slowly-moving Crustacea, found in evct·y sea, which conceal themselves under stones near the shore. Doctot· Leach has fot·mecl a genus with cet·tain species-ltexapus Latr. ;-longicornis, Id .,-Bluteli, Risso, Ct·ust., I, 7, &c., which he calls PrsiDIA. According to Dcsmarest, however, it does not differ in any appreciable chat·acter. Some of them are remarkable for their extremely large and pilose or ciliated forceps. Such are, 1. The Porcellane la1'ges pinces; Can· cer platycheles, Penn., Drit. Zoo!., IV, vi, 12; Het·bst., XLVII, 21 where only the external margin of the fo•·ceps is pilose and the neal'ly naked thorax is rounded; it is found on the rocks in the seas of Europe. 2. The P. ltirta, Lam., the whole .superior surface of whose fo1·ceps and thorax is pilose, and where the lattet· is nearly oval and becomes thinner anteriorly. It was brought ft·om King's Island by Messrs Peron and Lesueur. The forceps of the others at·e glabrous. Such is the Cancer hex· apus, L.; Herbst. XLVII, 4·. The thorax is marked with short, transvet·se, and slightly ciliated lines; the front trifid, with its mid· die tooth finely notched. The claws are covered with little blood· red scales and gt·anules, the fingers sepat·atecl and without internal dentations. It inhabits European seas(~). (1) .lEglee lisse, Desmar., Cons1der, xxxiii, 2; Latr., Encyclop. Method., Atl., d'Hist. Nat. cccviii, 2. (2) See the article Porcellane, Nonv. Diet. cPHist. Nat., Ed., ll; and I>esma.r., Consid, suP les Crust., p. 192-199. DECAPODA. 65 The genus MoNOLEPrs, Say,-Journ. of the Acad. of Nat. Sc. of Philad., 1, 155; Desmar., Consid., p. 199 and 200, appears to constitute the passage from the Porcellame to the ~egalop~s. !t ap-roaches the first in the two posterior feet, and m the dtrectwn of ihe tail. But this tail has but six segments, and the eyes are very large as in the second. It would also appear that the lateral fins of the end of the tail resemble those of the latter. The remaining Crustacea of the same division differ f~·om the ~receding in their posterior feet, which are similar to thtnr precedmg ones in form, proportion and uses, or equally ambulatot·y .. They are also removed from them by the greater thickness and hetght of the body, the shortness of the lateral antennre, the smallness of the claws, the large eyes, and lateral fins of the tail which are composed of a single lamina. This tail is extended, narrow, and simply bent under near its extremity. MEGALOPus, Leach.-Macropa, Latr., Encyc. Four species are known, three of which inhabit European seas and the fourth the Indian Ocean(l) whence it was sent to Paris by the late M. Leschenault and Messrs Quoy and Gaymard. In our second division of the .A.stacini, Latr., will be comprised those which have five pairs of false feet, · the mediate antennre straight or nearly so, salient, projecting, and termi?ated b! two filaments as long as theit· peduncle, or longer; and whtch, a smgle subgenus excepted-Gebia-have the four or six anterior feet terminated by a didactyle hand. Their tail is always extended; their two posterior feet are never more slender than the preceding ones, nor folded. The peduncle of the lateral antennre is frequently accompanied by a scale. Some of them, as well as others of the ensuing section, inhabit fresh water. Those in which the first four feet, at most, terminate in two fin-gers · whose lateral antennre never have a scale at the base; and whe:e the external leaflet of the lateral fins of the end of the tail presents no transverse suture, will form a first subdivision. Most of their feet are ciliated or pilose. They inhabit salt-water and conceal themselves in holes which they excavate in the sand. Sometimes the index or immovable finger-formed by a projection of the penultimate joint, of the claws, is very evidently shorter (1) For the European species, see Desmar., Consid., p. 200-~02, and pl. xxxiv, ~~ of the same work. VoL. III.-l |