THOUSANDS OF FATHOMS 219 
a podobranchia to the second maxillipeds, and there are 
no traces of pleurobranchiz although pleurobranchiz are 
developed on six pairs of appendages. ‘These are riddles 
which those who have specimens to compare with the de- 
scriptions may be able to solve. 
Aristeus, Duvernoy, 1841, is distinguished from Peneus 
chiefly by the circumstance that on the second and third 
maxillipeds and the first three trunk-legs it has the podo- 
branchize which the other is without. Aristeus antennatus 
(Risso) occurs in the Mediterranean and Atlantic, and is 
described as having a smooth pleon. 
Hepomddus, Spence Bate, 1881, is distinguished from 
Aristeus by a hepatic tooth on the shoulder of the carapace. 
Hepomadus qlacialis, of which Spence Bate’s figures are 
given in the adjoming Plate on a reduced scale, was taken 
near Yokohama at the frigid depth of 1,875 fathoms. 
Several new genera from Atlantic exploring expedi- 
tions have been described in recent years by Professor S. I. 
Smith, as Hymenopenceus, 1882, meaning the membrana- 
ceous Peneeus, Amalopenceus, 1882, which, at least in the 
type species Amalopeneus eleqans, has only the sixth seg- 
ment of the pleon carinate. Some of the lately described 
genera have names alluding to the great depths from which 
they were obtained : Benthesicyjmus, Spence Bate, 1881, 
Benthecétes, S. I. Smith, 1884, Benthonectes, 8. I. Smith, 
1885, all meaning those that dwell or swim in the abysses 
of the billowy ocean. Benthesicymus has a submembran- 
ous integument, exopods to the limbs as in Penceus, podo- 
branchiz as in Aristeus, and the last two pairs of trunk- 
legs longer than the preceding pairs. One of the species, 
Benthesicymus pleocanthus, Spence Bate, was trawled from 
a depth of 3,050 fathoms in the North Pacific, while other 
specimens were taken twenty degrees further south in the 
smaller depths of 450 and 1,050 fathoms. Benthonectes is 
specially characterised by the multiarticulate flagelliform 
dactyli, that is the subdivided terminal joints, of the last 
two pairs of trunk-legs. Xiphopeneus, 8. I. Smith, 1885, 
and Benthecetes have a corresponding peculiarity in the 
propodi or sixth joint of the same limbs. In some of the 
