54. DR. H. J. HANSEN ON CRUSTACEANS [ Jan. 20, 
antenn. ped. = peduncle of the antennule; mxp.’-mxp.*’=the 
second and third pair of maxillipeds; trl.\-trl.’=the first to the 
fifth pair of trunk-legs; br.=the first, br." =the second branchia 
above the same legs; ext. br. of urp.=external branch of the 
uropods. 
I. Notes on the Species of Petalidium and Sergestes. 
a. PETALIDIuM Bate. 
To this genus Bate has referred only one species. It will be 
convenient to deal with the characters of the genus together with 
those of the species. 
PET. FOLIACEUM Bate, pp. 348-50, pl. lx. (Plate XI. figs. la—1g.) 
Bate mentions five specimens from two stations: Stat. 146, 
lat. 46° 46’ S., long. 45° 31’ B., 1375 fathoms; and Stat. 159, lat. 
47° 25' S., long. 130° 22’ E., 2150 fathoms. All these specimens 
are at present in the Museum, but even Bate’s text and his figure 
of the entire animal show that most of the appendages presenting 
specific characters are wanting or have been mutilated. Bate 
writes (p. 849): “The great distinction between this genus and 
Sergestes exists in the form, character, and arrangement of the 
branchial plumes, which consist of a series of plates and eylin- 
drical filaments, situated side by side in a series of rows at right 
angles to the stalk. There is but one plume to each of the five 
anterior somites of the pereion, the posterior two somites having 
none; between some of the somites is a large foliaceous plate.” 
But this description is difficult to understand: his figure 3, 
representing the branchie, is defective, and his tabular view 
(p. 349) is wrong. He was of opinion that the foliaceous plates— 
of which he had seen only three—were pleurobranchie, while the 
“branchial plumes” were arthrobranchiz; but this is incorrect: 
they are decidedly pleurobranchie asin Sergestes. Petal. foliacewm 
Bate differs from all species of Sergestes in one quite unimportant 
feature, that no trace of branchie is found above trl.*, and in one 
important character, viz., the structure of the pleurobranchial 
plumes. This structure is very interesting (fig. le). The most 
developed branchie are, as usual, those above trl.* and trl.*; each 
of these consists of an anterior and a posterior half, and each half 
of five (to six) transverse rows of branchial plates, generally five 
or six in each row, and these plates (some of the lowest excepted) 
are directed upwards. ‘The pleurobranchie above mxp.’ and 
especially trl.* are less developed, with a lower number of trans- 
verse rows, and partially with a lower number of plates in the 
rows. The pleurobranchial plumes in VPetalidiwm look very 
different from those in Sergestes; the real differences are: a 
much lower number of rows, a much lower number of plates in 
the rows, and that the plates are much larger, curved upwards, and. 
look much more independent. Behind the upper part of each of 
these four pleurobranchie originates a pleurobranchial lamella (/.), 
