REPORT ON THE CRUSTACEA MACRURA. xli 



than the third; it has the carpos single-jointed, which is also the case in the Dendro- 

 branchiata, the only difference being that in this division the second resembles the 

 first, but is slightly larger and a little longer, corresponding in size between the first 

 and second pairs. 



We find that this is continued, but to a less degree, in the Sergestidae, in which 

 family the second pair corresponds more nearly with the third than with the first. 



In the Phyllobranchiata the several variations of form are more marked and in 

 stronger contrast. In the genera belonging to the families of the Nikidae, Alpheidae, 

 Hippolytidse, and Pandalidse it is long, slender, minutely chelate, and has the carpos 

 multiarticulate, the articuli varying in number and length in various species or 

 genera. 



In the Crangonidse it is short, slender, and feeble, and the carpos is not multiarti- 

 culate, and this is also the case in all the genera belonging to the Palaemonidse, only 

 here it is larger and often very much longer than the first pair; so it is in Typton, 

 Pontonia, and Oodeopus, while it differs in Nematocarcinus in being small and having 

 the carpos long and slender, and not multiarticulate. 



The differences between the multiarticulate condition of the carpos and those in 

 which it is uniarticulate is so marked that I have separated them into two tribes, under 

 the names of the Polycarpidea and Monocarpidea. In the Haplopodea all the legs are 

 uniform. 



The TJiird Pereiopoda. — The third pair of pereiopoda is chelate in all the genera 

 of the Trichobranchiata, except in the group Synaxidea, in which none of them are chelate 

 except the posterior in the females, the first being only subchelate in some genera. 

 This part is generally small and subequal to, or smaller than, the second pair. 



This chelate condition also exists in some of the aberrant forms, but in others, as 

 in Thalassina, Eiconaxius, &c, it is simple. In the family Stenopidse the third pair 

 is large and chelate, having the hand long and slender in Stenopus, broad and thick in 

 Sponyicola, and in each longer than the preceding, thus acquiring the character and 

 appearance of the Dendrobranchiata, whilst in the compressed rostrum it much resembles 

 in external appearance the Phyllobranchiata. 



In the Dendrobranchiata this pair is the largest and the longest of the chelate feet, 

 and is universally formed on the same type as the two preceding. In the Sergestidse 

 it is chelate, but only minutely, as it is also in Lucifer, and in both cases it is buried 

 in a brush of hairs. I have not had an opportunity of examining it in Acetes. 



In the Phyllobranchiate forms the third pair of pereiopoda is universally simple. 



In the Crangonidse it is long, slender, and styliform ; in the Nikidae it resembles 

 the succeeding and is less styliform than in the Crangonidse. It is also styliform in 

 the Pasiphaeidae but comparatively less so than in the Crangonidas. In several genera 



(ZUOL. CHAIX. EXP. PAUT LII. 1S8S.) Fff/ 



