18 G- O. Sårs. 



a very delicate membranous lappet of conical form and finely 

 ciliated on the edges. From its position, this lappet 

 would seem to answer to the endopodite in the preceding 

 pairs. The exopodite has likewise the form of a membranous 

 lappet originating from the stem outside the endopodite, 

 with which it is partly connected. It has the outer edge 

 clothed with delicate hairs, and projects at the end below 

 into 2 setiform appendages, the inner of which is well de- 

 fined at the base, whereas the outer forms the immediate 

 continuation of the lappet. Both these appendages point 

 straight below and are finely ciliated. 



The last pair of legs (fig. 10) are very unlike the pre- 

 ceding pairs, and are exclusively branchial in character. They 

 each terminate in a comparatively large rounded vesicular 

 body, which undoubtedly represents the epipodite. The 

 whole distal part of the stem, together with the endopodite, 

 exopodite and masticatory lobe, is of course wholly wanting 

 in this pair. On the other hand, the remaining part of the 

 stem is expanded in a peculiar manner, forming above the 

 epipodite a rather large and very delicate, posteriorly- ex- 

 tending plate. This basal plate, of which no trace is found 

 in the genus Macrothrix, projects into 3 linguiform lobes 

 pointing in different directions, and fringed with delicate cilia, 

 and in the living animal is found to perform very regular, 

 almost rhythmical oscillations. 



The caudal part of the body, or tail proper, as usual, 

 is abruptly bent downwards, pointing even somewhat for- 

 wards, when at rest (see PI. 1, fig. 1). It is much more freely 

 mobile than in the genus Macrothrix, admitting of being al- 

 most wholly extended from the shell, which is not the 

 case in that genus. In form (see PI. II, fig. 11), it is ob- 

 long quadrangular, with the anterior and posterior edges al- 



