6 W. T. CALMAN. 
A difference which may possibly be of greater importance than any of those 
mentioned above exists, as Prof. Coutitre has pointed out, in the branchial system. 
In addition to the five pleurobranchie possessed by C. antareticus, C. franciscorum 
has on each side a well-developed arthrobranchia at the base of the third maxilliped. 
The statements made by various writers as to the gill-formula of the common shrimp, 
and of the genus of which it is the type, are curiously conflicting. Although 
Huxley, in 1878, Boas, in 1880, and Claus, in 1886, gave the number of gills in 
C. vulgaris correctly as six, more recent authors seem to have overlooked the 
arthrobranchia of the third maxilliped, which, although small, is not at all difficult 
to see. Sars, in 1890,* gives among the characters distinguishing Crangon from 
Pontophilus, the presence of five gills in the former and six in the latter genus, 
and this statement is copied by Mr. Stebbing.t Ortmann, in his revision of the 
Crangonide in 1895,f names a number of species of Crangon which he has examined 
and found to have only five gills. One of the names mentioned, ‘ typicus,” 
does not appear elsewhere in the paper, but it may be conjectured that it refers 
to the typical form of the species C. vulgaris. Two other species on the list are 
C. afinis and C. franciscorum. In these three species, and also in C. allmanni and 
C. nigricauda, I find, on the contrary, that the arthrobranchia is well developed. In 
the absence of trustworthy data as to the occurrence of this gill in the other species 
from the northern hemisphere, it is not possible to estimate the importance to be 
attached to its absence in C. antarcticus. It may be noted, however, that it is absent 
in the characteristically Arctic genus (or subgenus) Sclerocrangon, which is otherwise 
not very sharply defined from Crangon, and to which, in its strongly sculptured 
carapace, the present species has some resemblance. Prof. Coutiére, in his preliminary 
notes on the Decapoda of the ‘Belgica,’ has called attention to this resemblance to 
Selerocrangon ; but he suggests, with some hesitation, the establishment of a new 
subgenus, Notucrangon, for the Antarctic species. I have not been able to examine 
the structure of the male pleopods, to which he attaches some importance, but the 
other characters which he mentions do not seem to me to justify this step. 
Larve.—A number of larve of this species were collected, all in a stage of 
development corresponding to the “last larval stage” of Prof. Sars. The rostrum is 
very long and slender, extending well beyond the eyes. There is a small median dorsal 
tooth on the carapace, about midway between the back of the orbit and the “ cervical ” 
groove, and a little in front of it is a rounded papilla (represented in some of Sars’s 
figures) probably representing the problematical “dorsal organ” of some Euphausid 
larve. The abdomen is unarmed, except for the paired spines at the posterior end of 
the fifth somite, which are long and slender, almost as in Sars’s figures of the larvee of 
Pontophilus, and, as in that genus also, the sixth somite is very long. The telson is 
very large, in the form of an almost equilateral triangle, with the posterior margin 
* Arch, Math. Naturvid, xiv. (1890), p. 153. + Hist. Crustacea (1893), p, 227. t Proc, Acad. Nat. Sci,, 
Philad. (1895), p. 175, 
