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



The second pair is long and well developed, being nearly three-fourths the length of 

 the animal, but not especially robust ; the terminal two joints are slender and fringed 

 with hairs. 



The first pair of pereiopoda is two-thirds the length of the second pair of 

 gnathopoda. The upper margin of the ischium is armed with a small tooth, and a 

 fasciculus of small hairs or spines is implanted at the propodal articulation of the carpos ; 

 it is fringed with hairs, those on the lower or posterior surface being very long, especially 

 towards the base. The propodos is also ciliated on both sides, but the hairs are not so 

 long. The second and third pairs of pereiopoda are long, quite as long as the second 

 pair of gnathopoda, and have the carpos and propodos fringed with long hairs, which are 

 elevated on small prominences that give these appendages a multiarticulate appearance ; 

 each terminates in a small rudimentary chela. The posterior two pairs are feeble, the 

 penultimate reaching nearly as far as the extremity of the meros, while the ultimate is 

 small and rudimentary. 



The pleopoda are robust and tolerably long, gradually decreasing in length posteriorly, 

 but not increasing in diameter, as they frequently do in various species. 



The rhipidura is quite as long as the sixth somite of the pleon ; the outer margin 

 near the middle is armed with a very minute tooth, posterior to which it is fringed with 

 strong, ciliated hairs, similar to those on the inner branch. 



Length, 12 mm. (0"5 in.). 



Observations. — The specimen from which I have taken the preceding description 

 corresponds so closely with that of Kroyer, that I do not hesitate to identify them as being 

 the same, even though the localities are so widely separated; yet under a moderate 

 magnifying power there is a difference that must not be passed over. In Kroyer's 

 figure the rostrum is shown to be horizontal, in the same line as the dorsal surface of the 

 carapace ; in that which I have described the rostrum is horizontal but it is elevated 

 slightly on a crest above the dorsal surface, on which, above the orbital margin, a 

 minute point exists which is only observable under 60 diameters magnifying power. 

 So similar are all the other features that I am induced to believe that these details were 

 probably not appreciable under a low magnifying power, and therefore not described as 

 being present in Kroyer's typical specimen. 



A specimen taken in the North Atlantic (April 29, 1876) has the rostrum more 

 than half the length of the ophthalmopod, and the chelae at the extremity of the second 

 and third pairs of pereiopoda are not developed, as if the animal were still in an immature 

 condition, which appears to be the state of Kroyer's specimen, if we may judge from 

 his figure. In that which I have figured the chelae are so minute as only to be deter- 

 mined by a considerable magnifying power, which may be the case with Kroyer's 

 specimens also. 



