4J2 



CRUSTACEA. 



British species, having the frontal rostrum not extending beyond the peduncle of the superior antennae, and 

 nearly straight. 



[Other genera have been proposed by Risso, Leach, P. Roux, and M. Edwards, founded upon variations in the 

 form and proportions of the legs.] 



Pasipfxea, Savigny, is a very interesting genus, allied to the preceding in the upper antennae, terminated by 

 two filaments ; the four fore-legs terminated by a didactyle claw, but [differing from all the other Carides] in 

 having the external base of the legs furnished with a thread-like appendage; the claw-legs are larger, nearly equal 

 in size, very slender, and filiform ; the body is very long, very compressed, and very soft. Type, P. Sivado, Risso. 

 Found in the Mediterranean, especially in the Bay of Nice, where it is very abundant.* 



The fifth and last section of the Macroura — that of the Schizopoda — appears to unite them with 

 the subsequent order. The legs are very slender, like flattened threads, and not furnished with claws, 

 but having a longer or shorter lateral appendage arising on their outside near the base, and [the legs 

 are] fitted only for swimming. The eggs are borne between them, and not under the tail. The ocular 

 peduncles are very short. As in the majority of the Macroura, the front is prolonged into a kind of 

 rostrum. The carapax is very slender. The tail terminated, as is customary, in a swimmeret. These 

 Crustacea are minute and marine. 



In some, the eyes are very apparent ; the lateral antenna; furnished with a scale ; the intermediate 

 ones terminated by two filaments, and composed of many minute joints, as in the preceding.f 



Mysis, Latr., has the antennae and legs uncovered ; the carapax long, nearly square, or cylindrical ; the eyes 



close together; and the legs capillary, and formed of two thread-like fila- 

 ments. Type, M. Fabricii, Leach; Cancer scutatus, O. Fabricius. 



[The species of Mysis are termed Opossum Shrimps, from their singular 

 economy of carrying their eggs and young in a large pouch, with membranous 

 envelopes, beneath the thorax and between the thoracic legs. Their structure 

 has been fully investigated by Thompson in his Zoological Researches. In 

 the Encyclopedic Methodique are also some figures communicated by Dr. 

 Leach to Latreille, and evidently intended for the Malacostraca Britannica 

 of the former author, but which were never published by him. 



Two other genera, nearly allied to Mysis, have been proposed by Thompson, 

 founded upon oceanic species, namely : — • 



Cynthia, having branchiae attached to the subabdominalfins ; and Noctiluca, 

 founded upon a luminous species, but not described with sufficient precision, 

 and omitted by M. Edwards. 

 Thysanopoda (Edwards), in which there are also eight pairs of bifid natatory feet, but the branchiae are in the 

 form of many-branched, membranous appendages, at the base of the true legs. 



The genera Phasmatocarcinus, Tilesius (in the Neue Annalen Wetterausch Gesellschaft, vol. i.), considered by 

 Thompson and Edwards as undescribed, and named by the former Lucifer (Leucifer, Edwards), and that of Podop- 

 sis by Thompson, are amongst the most singular of known Crustacea, having a filiform body, with very large 

 globular eyes placed at the extremity of very long and laterally extended foot-stalks; and the legs are exceedingly 

 slender and short. According to Slabber, whose figure of one of the species has been overlooked by all Crustace- 

 ologists, there are eight pairs of legs of equal size.] 



Cryptopm, Latr., has the carapax subovoid, swollen, bent under at the sides, enveloping the body, as well 

 as the antennae and legs, having only on the under side a longitudinal slit. The eyes are wide apart. The 

 legs are like flattened threads, with a lateral appendage. Type, C. Vefraneii, Latr. Mediterranean. 



In others, the eyes are hidden. The intermediate antennae conical, exarticulated, and very short. The lateral 

 antennae composed of a peduncle and a filament, without distinct articulations : their base is not protected by a 

 porrected scale. 

 Mulcio, Latr., has the body very soft ; thorax ovoid ; legs like flattened threads, the majority with an ap- 



Fig. 8. — Mysis vulgaris, about twice tin 



natural length. 



a, one of the bind legs. 



* [Many additional genera have been added to the Carides by Poly- 

 dore Roux in his Mtmoire sur la Classification des Cruttacd de la 

 Tribu des Salicoquet, Marseilles, 1831 ; and by Milne Edwards in the 

 Annates des Sciences Naturella, and Hist. Nat. des Crustacis. Of 

 these it will be necessary only to notice those of Sicyonia, nearly 

 allied to Peuteus, but differing from it and all the other genera in 

 having no appendages to the false subabdominal legs, and in the modi- 

 fications of its respiratory apparatus, there being only eleven pairs of 

 brain in,; instead of eighteen. Sergcstes atid Acctes — in which the 

 posterior pair of true legs is almost rudimental, or entirely obsolete, 

 the outer pair of foot jaws being immensely developed, so as to consti- 

 tute an anterior pair of legs to supply their place. These genera are 

 founded upon exotic species.] 



[Here terminates, in the system of M Edwards, the great order of 

 Decapod Crustacea, which, in his Hist. Nat. drs Crustuth, is suc- 

 ceeded by an appendix consisting nf " Decapudes douteux," compris- 

 ing the genera Zoca, Cerataspis, Mulcio, and Posydon. With respect 

 to Zoea, I have clearly proved in my Memoir, published in the Philo- 



sophical Transactions, that it is a Decapod ; and therefore the observa 

 tions of Latreille, at the end of the Decapods, cannot be adopted.] 



f [The Schizopoda having, since the publication of the second edi- 

 tion of this work, been well investigated by Edwards and Thompson, 

 have been found to be more nearly allied to the order StomapoUa, 

 although presenting so near a resemblance to the Carides. This inno- 

 vation was adopted by Latreille himself in his fours d'Elltomvlogie, 

 in which this author has proposed to give those Podopthalmous 

 Crustacea which are destitute of thoracic internal branchhe, but 

 otherwise resembling the Carides, the sectional name of Caridioides, 

 indicative of their analogy with the last-named group. The typical 

 genus Mysis is especially interesting, on account of the complete 

 transformation of all tile three pairs of foot-jaws into legs, so that, to- 

 gether with the five pairs of true legs, there are eight pairs ol loco 

 motive organs ; and as each of these is divided from the base by the 

 addition of a lateral appendage, these animals may be said to have not 

 fewer than thirty-two legs. J 



