REPORT ON THE CRUSTACEA MA CRURA. 825 



The second pair of antennae has the peduncle robust, and carries a broad scaphocerite 

 that is rounded at the extremity, and armed on the outer distal margin with a strong tooth. 



The mandibles have a large and broad psaKstoma that is slightly serrate, and 

 continuous with a small, smooth, lunate, molar process, and carry a stout three-jointed 

 synaphippd, of which the terminal joint is short and spatuliform. 



The three pairs of siagnopoda correspond generically with those of Acanthephyra, as 

 do also most of the other appendages, such variations only existing as may be supposed 

 to accord with specific changes. 



A. Milne-Edwards says that " the first pair of pereiopoda is longer than the second ; 

 they are both didactyle," but in all our specimens of the several species the first pair of 

 pereiopoda is shorter than the second. The third and fourth pairs of pereiopoda are long, 

 and have the propodos more slender than the preceding joints, and the dactylos long, 

 styliform, and slightly curved ; the fifth pair resembles the two preceding, but terminates 

 in a short, almost obsolete, dactylos, embedded in a thick brush of ciliated hairs. 



The pleon has the dorsal surface strongly cariiiated, and is generally produced to a 

 tooth on the third and following somites. 



The telson is dorsally flat or grooved, and does not extend beyond the length of the 

 inner plates of the rhipidura. 



A. Milne-Edwards says that " the rostrum is remarkably short and slender, and 

 carries about eight teeth above and the same below ; it does not reach beyond the 

 scaphocerite." This is correct of four out of five of the Challenger species, but 

 Notostomus longirostris, as well as his own Notostomus elcyans, has the rostrum longer 

 than the scaphocerite, and all our specimens have the dentation on the former more 

 abundant than described by A. Milne-Edwards from his type, Notostomus gihbosus. 



There are several details in the above description which disagree with that given by 

 A. Milne-Edwards, above quoted, but I have had the opportunity of showing the plates 

 of this work to that author, and also of examining the animals from which his description 

 was taken, and I feel assured that the various forms belong to the genus he has described, 

 and I therefore adopt the name that he has proposed. 



The branchige closely agree with those of Acanthephyra. The several pleurobranchiaj 

 are implanted so near the pereiopodal articulation, that it was only in the larger specimens 

 I could be certain that they do not spring from the articulating membrane. The plumes 

 are well formed and not so much laterally compressed, more especially the pleurobranchise, 

 as in Acanthephyra. 



The branchial arrangement of this genus is shown in the following table : — 



Pleurobrancbiae, . . . ...1 1 1 1 1 1 



Arthrobranchiae, . . . ...1 1 1 1 1 



Podobranchiae, . . . 1 



Mastigobranchise, . . . 1 1 1 1 1 



hi k 1 m n o 



(ZOOL. CHALL. EXP. — PART LII. — 1887.) Fff 104 



