230 THE VOYAGE OF H.M.S. CHALLENGER. 



The second pair is three-branched; the first branch carries a broad mastigobranchial 

 plate, the next two are biramose and foliaceous, and the third is truncate. 



The third pair of siagnopoda is five-branched. The first branch carries a broad but 

 not very large mastigobranchial plate ; the second is biramose and foliaceous, and supports 

 externally a foliaceous ecphysis, and the terminal one is narrow, slender, cylindrical and 

 triarticulate. 



The first pair of gnathopoda is seven-jointed, short, and subpediform ; the terminal 

 three joints are reflexed, and flattened on the inner or approximating margin. The 

 second joint or basis carries a very long two-jointed ecphysis, which has the first joint 

 short and cylindrical, the second long, flat, multiarticulate, and fringed on each side 

 with long ciliated hairs. 



The second pair of gnathopoda is seven-jointed, pediform, and long; it frequently 

 reaches nearly as far as the distal extremity of the ophthalmopod. 



The first three pairs of pereiopoda are chelate, gradually increasing in length, and each 

 of them carries a basecphysis. 



The posterior two pairs are not longer than the preceding, are subequally slender, 

 and terminate in simple dactyli. 



The pleopoda are large and powerful, terminating in two foliaceous branches in every 

 pair except the first, which in the male carries attached to the base a large membranous 

 appendage that I call " petasma," which in the female is reduced to a small and rudi- 

 mentary condition. 



The rhipidura is large and powerful ; the lateral plates are broad and foliaceous, and 

 strengthened by a longitudinal ridge that traverses the external margin of the outer 

 plate, and terminates in a sharp tooth. 



The telson is tapering, and liable to variation in its length and armature. 



Observations. — This description coincides with the first division of the genus 

 according to M. Milne-Edwards, or with those in which the first pair of antennae does 

 not reach beyond the posterior margin of the carapace. As here limited the branchial 

 arrangement differs from those species in which the flagella of the first pair of antennae 

 reach beyond the posterior margin of the carapace. 



This genus was founded by Fabricius on the Mediterranean species, Penaeus 

 caramotus, which in external character is so closely allied to Penaeus canaliculatus from 

 Japan, described by so many naturalists, that I have accepted it as the type of my 

 description. 



Geographical Distribution. — This genus appears chiefly to inhabit the warmer seas. 

 Species exist in the Atlantic and Pacific Oceans ; in the former, ranging as far north as 

 to be occasionally met with on the southern shores of Britain, and as far south as 

 Brazil ; in the latter, from Japan to the southern shores of New Zealand. 



