55 



appendage of the mandibular palps replaced by a single strong seta. Palps of 

 maxillipeds short and stout, with the 2 outer joints very small. Posterior legs 

 with 3 apical setae, one of them very coarse, almost spiniform, and evenly 

 curved. Caudal rami rather broad at the base, but rapidly tapering to an obtuse 

 point carrying the very short, hamiform curved apical claws, and apparently 

 wanting the usual small bristle in front of the claws, 



Male much smaller than female, and having the shell still narrower, with 

 the posterior extremity more exerted. 4 of the setae attached to the anterior 

 antennae in the middle of the terminal part much produced and generally re- 

 curved along the back of the shell. Natatory setae of the posterior antennae 

 prolonged in a similar manner. Palps of maxillipeds rather powerfully developed, 

 with the propodus considerably dilated at the base and the dactylus short and 

 stout, unguiform. Copulative appendages narrow oblong in form and obtusely 

 rounded at the tip. 



Colour in both sexes a pure white. . 



Length of adult female amounting to 0.69 mm., that of male scarcely 

 exceeding 0.60 mm. 



Remarks. This form, being that at first described, ought of course to be 

 regarded as the type of the present genus. It may be easily recognised from 

 any of the other species by the almost cylindrical shape of the shell in the 

 female, this character having indeed given rise to the specific name proposed. 

 Of the 5 Mediterranean species recorded by G. W. Mtiller, A. caudata seems, 

 in the shape of the shell, to come nearest to the present species. 



Occurrence. \ have met with this Ostracod occasionally in several places 

 on the Norwegian coast, from the Christiania Fjord to Trondhjem, and Norman 

 also records it from Finmark (Hammerfest). It is generally found in moderate 

 depths ranging from 10 to 30 fathoms, on a muddy bottom, and, in spite of 

 its small size, may be easily detected by the pure white colour of the shell 

 and by a peculiarity which it has in common with some other Ostracoda, viz., 

 that, on coming in contact with the air, it remains floating on the surface of 

 the water. The females are quite devoid of swimming power, crawling slowly 

 on the bottom, like the Cytheridae. The males, however, may perhaps lead a 

 more free existence, as could be inferred from the peculiar prolongation of 

 some of the setae attached to the antennae. 



Distribution. British Isles (Brady). 



Fossil in the postglacial beds of Scotland, 



