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



female, and six on the lower; but, as Milne-Edwards' specimens were obtained from 

 floating weed in the Indian Ocean, the two sexes in that region may more closely 

 resemble each other in their ornamentation, and thus the rostrum may have eleven 

 teeth on the upper margin of the rostrum and be scarcely dentate at all on the lower. 

 The serrature in our typical specimens is not very strong, and in many it is feeble 

 enough to fulfil the description of Milne-Edwards. 



Desmarest describes and figures his species, Leander erraticus, as being strongly 

 dentate above and " au contraire sans dents en dessous." In all other features both the 

 figure and the description correspond with Palsemon natator, Milne-Edwards, and it is 

 probably a variety in which the armature on the lower margin of the rostrum is more 

 than usually undefinable. 



Palsemonella, Dana. 



Palxmonella, Dana, U.S. Explor. Exped., Crust., p. 582. 



„ Kiugsley, Proc. Acad. Nat. Sci. Philad., p. 425, 1879. 



Kesembles Palsemon, but has the rostrum long, thin, and slender, the first two 

 pairs of pereiopoda chelate, the second one longer than the first. Mandibles furnished 

 with a two-jointed synaphipod. Two of the flagella of the first pair of antennae united 

 nearly to their tips. 



The carapace is furnished with two teeth below tbe orbit, in nearly the same 

 horizontal line. 



The second pair of gnathopoda is slender, as in Palsemon. 



The first pair of pereiopoda is very slender. The second pair is moderately robust, 

 with the hand nearly cylindrical, and hardly stouter than the preceding part of 

 the leg. 



The foregoing is a close transcription of Dana's diagnosis of the genus. Eingsley ' 

 appears to determine the genus as distinct from Palsemon by the synaphipod being 

 Particulate, and the first pair of antennae biflagellate, one flagellum having the apex 

 bifid ; he says that in Palsemon it is triflagellate, which is not the case, as may be seen 

 in the typical species as well as in Palsemon affinis (p. 783). 



Observations. — There is but a single specimen, and that a young one, in the 

 Challenger collection, and I therefore have not had an opportunity of examining the 

 oral appendages in detail ; but I accept the genus on the character of the mandibles, 

 the form of the rostrum, and the presence of a hepatic tooth on the carapace, as given by 

 Dana and Kingsley. 



Geographical Distribution. — There are but two species known, and these were both 

 taken in the Oriental seas. 



1 Loc. cit., p. 425. 



