An examination of the illustrations of the appendages of Pontostratiötes given by Brady 

 in the 'Challenger' Report shews that there is a close relationship between that genus and Aegisthus, 

 described and illustrated by Giesbrecht in bis Xaples Monograph. The two genera are distinct 

 from any of the Harpacticoida and oughjt, I think, to be placed under a separate family. I 

 have recently had the privilege of examining a specimen of a Copepod identical with Brady's 

 Pontostratiötes abyssicola and tind that this opinion appears quite reasonable. 



The chief differences between the two genera, apart from the presence or absence of 

 cephalic and thoracic spines, are to be found in the jointing of the exopodite of the antennae 

 and in the development of the mandible palp. The exopodite of the antennae of Pontostratiötes 

 is four-jointed. It is only one-jointed in Aegisthus. The mandible palp of Pontostratiötes is well 

 developed and two-branched. The exopodite is four-jointed. The mandible palp of Aegisthus 

 is quite rudimentary and unbranched. The antennules, maxillae, first pair of maxillipedes and 

 the five pairs of feet are nearly identical in the two genera. 



The long so-called furcal setae in the two genera may really represent the furcal joints, 

 because the long setae in perfect examples of Aegisthus terminate in one plumose and two 

 simple setae. These terminal setae appear to be articulated to the long setae just as in normal 

 furcal joints. 



Genus Aegisthus Giesbrecht, 1891. 



The body is slender and of moderate length. The forehead is produced into a sharp 

 immovable rostrum. The principal furcal seta is of great length. It is in the form of a slender 

 setiferous spine with a jointed apex that carries a plumose seta. The antennules are rather 

 slender and six or seven-jointed. The first joint has a distinct knob at the distal end of the 

 upper margin. The exopodite of the antennae is small and one-jointed. The mandible has 

 a well developed biting edge and a very rudimentary palp. The maxillae consist of a broad 

 biting part and one digitiform lobe. The first pair of maxillipedes is rather large and five-jointed. 

 The two basal joints are moderately long. The three apical joints are short. The distal end 

 of the upper margin of the second basal joint is furnished with a slender claw. The second 

 pair of maxillipedes is lamelliform and two-jointed. The second joint is very short. The exopodites 

 and endopodites of the first four pairs of feet are three-jointed and of nearly equal length. 

 In some specimens the exopodite and endopodite of the first pair of feet are rather indistinctly 

 three-jointed. The fifth pair of feet is moderately long and slender. It is indistinctly two jointed. 



Two species belonging to this genus were represented in the plankton collected by the 

 'Siboga' in the Malay Archipelago. 



1. Aegisthus aculeatus Giesbrecht. 



Aegisthus aculeatus Giesbrecht, 1891, p. 476. 



Aegisthus aculeatus Giesbrecht, 1S93, p. 573, pis. 46 & 49. 



Aegisthus aculeatus I. C. Thompson, 1903, p. 33. 



Aegisthus aculeatus Cleve, 1904, p. 185. 



Aegisthus aculeatus van Breemen, 1908, p. 181, fig. 195. 



233 



SIBOGA-EXI'EDITIE XXIXO. 3° 





