REPORT ON THE CRUSTACEA MACRURA. 33 



posterior pair of pleopoda has the outer branch much larger than the inner, and both 

 have the inner margin fringed with ciliated hairs, and the extremity furnished with hairs 

 and spines. 



The mastigobranchial plates and podobranchial plumes are entirely wanting, and so 

 also are the pleurobrauchise, and in this respect the character of the organs is consonant 

 with those of Callianassa, inasmuch as the only plumes that are present are the 

 arthrobranchial, which, however, appear to vary as to number, as shown in the following 

 formula : — 



Pleurobranchne, . . . . 



Artbrobranchiee, . . . . 22 21... 



Podobranehias, . . . . 



Mastigobranchia?, . . . . 



h i k 1 m 11 o 



A variation exists not only in the number, but also in the form of the structure, more 

 especially in that of the anterior plumes ; the tendency being to form large and broad 

 foliaceous plates at the base of the stem, changing in some cases rather suddenly into 

 slender cylindrical processes, that gradually shorten toward the apex of the plume. 



Unfortunately there was but a single specimen taken of this interesting little species, 

 and that in a very damaged condition. 



Comparing it with the species that we have just described as being taken at the 

 entrance of Torres Straits, in only 28 fathoms of water, — a locality that is almost 

 the antipodes of the other; the one in lat. 19° N. and long. 63° W., while the other 

 was taken in long. 10° S. and 142° E., — the similarity of the two is very remarkable. 

 The only distinctions by which I could positively determine the one from the other are 

 in the form of the rostrum, branchiae, and telson, and perhaps of the lateral caudal pleopoda. 

 In Cheramus oricntalis the telson has the posterior margin fringed with long ciliated hairs,, 

 and in the median line there is a very rudimentary point at the bottom of a slight 

 depression. In Cheramus occidentalis this depression exists, while in the median line 

 there is a well-defined straight tooth. 



The lateral caudal pleopoda have their armature, although strongly spinous, yet 

 scarcely as hooked in form as in Cheramus orientahs. 



On the inner branch of the third pair of pleopoda is a small stylamblys, rather more 

 pointed than in Cheramus orientalis, and fringed with small cincinnuli or booklets. 



With this species was taken an anterior right or large cheliped (PI. II. fig. 2k). It 

 appears to be rather too large to belong to the individual I have described, but it may 

 belong to another specimen of the species (see p. 29). 



The branchial plumes of the two species of this genus, which come from such 

 distant localities, are very instructive in their character. In Cheramus orientalis, 

 the arthrobranchia attached to the second pair of gnathopoda is very short, and carries a 



(ZOOL. CHALL. EXP. — PART LII. — 1886.) Fff 5 



