REPORT ON THE CRUSTACEA MACRURA. 23 



joint. The outer branch flat multiarticulate, the inner two-jointed — one cylindrical, the 



Other multiarticulate and flattened ; both fringed with a few long hairs. 



The sixth or posterior pair of pleopoda is biramose on a short basisal joint. The 

 branches are uniformly stiff and narrow, being of the same length as the telson, slender, 

 tapering, slightly curved and fringed with hairs, and form the lateral plates of the rhipidura. 



The branchial chamber is very large, as may be observed from the anterior position 

 of the cervical furrow, and the dorsally narrow and posteriorly still narrower gastric, 

 genital, and cardiac regions. The inner surface of the carapace is covered with a mem- 

 brane plicated in a series of fine ridges or folds, radiating from a position near which the 

 muscles of the mandibles are attached to the carapace. This membrane is smooth and 

 clean, and terminates on the interior surface at the posterior margin of the carapace, 

 where a series of thickly-set hairs form a fringe capable of assisting to afford a protec- 

 tion against the admission of extraneous matter. The floor, or pleural surface of the 

 same great chamber, is smooth and highly polished, and is not covered or protected by 

 any tissue. The surface is generally even, but a sudden depression corresponds with 

 cavities that hold the muscles of the gnathopoda. The enlargement or elevation of 

 the portion posterior to these appendages corresponds with the functional requirements 

 of the several pereiopoda. 



The branchial formula of this species is — 



Pleurobranchise, 



Arthrobranehiaj, .... 



Podobranchise, .... 



Mastigobranchise, .... 



There are no pleurobranchial plumes attached to either of the somites. There are two 

 arthrobranchial plumes attached to the articulations of all the appendages of the pereion 

 except the last pair of pereiopoda. There are only four podobranchise, and these are 

 appendages of mastigobranchial rods of a reduced and imperfect character. Six similarly 

 formed mastigobranchiae are attached to the six anterior appendages of the pereion, the 

 last, or fifth, pair of pereiopoda being without any branchial apparatus whatever. A 

 similarly formed mastigobranchia, being more important in character, extendiug in length 

 to a considerable distance within the branchial chamber, is attached to the second pair 

 of siagnopoda ; whereas the third or next succeeding pan' posteriorly has none. 



Observations. — The branchiae of this animal are of a peculiar character, and form an 

 interesting feature in their relation to the entire order to which they belong. 



The second pair of siagnopoda, as I have just stated, supports a long mastigobran- 

 chial appendage, that carries on its margin, more especially at the extremity, numerous 

 extremely long and tolerably stiff hairs of peculiar formation. They are generally straight 

 and rigid, but some are curved at the extremity. As a whole, these hairs gradually 



