os) 
Entomostraca from the Arctic Seas. 358 
collected off Kolguev in June. As one or two slight dif- 
ferences have been observed between these specimens and 
those obtained in the Firth of Forth, we submit the following 
remarks on these differences as well as on the otherwise 
close similarity of the Arctic and Scottish specimens. 
Figure 1 (Plate VI.) is a drawing of one of the Arctic 
female specimens; this specimen measures *78 mm. (q5 of 
an inch), and is thus proportionally larger than those from 
the Firth of Forth. 
The antennules and antenne (figs. 2 & 3), the mouth- 
appendages (figs. 4 to 7), and the first, second, and fifth 
pairs of thoracic feet (figs. 8, 9, & 12) are similar to the 
same appendages in the Scottish specimens. The third 
pair of thoracic feet have the inner branches three-jointed 
and armed with an elongated dagger-like terminal spine in 
addition to several plumose sete; but in the specimens from 
the Firth of Forth the inner branches of the same pair are 
only two-jointed, they are not provided with terminal spines 
but carry instead two slender apical sete ; it may be observed, 
however, that though the inner branches of the Forth speci- 
mens are only two-jointed, the end joint is long and may 
therefore consist of two coalesced joints, which, under the 
influence of the altered conditions to which the Arctic speci- 
mens may be exposed, have become distinct ; these altered 
conditions may also explain the difference in the armature 
of the branches. 
But in addition to this difference in the third pair of 
thoracic feet between the Arctic and Scottish specimens, 
there is the presence, in the Arctic specimens, of what appears 
to be a very small and rudimentary fourth pair of thoracic 
feet, each consisting of a small lamelliform basal joint, and a 
minute secondary one bearing two dagger-like apical spines 
(fig. 11). In the specimens from the Firth of Forth, on the 
other hand, the presence of a fourth pair has not been 
observed *. ‘This rudimentary fourth pair in these Arctic 
specimens is, perhaps, a more important difference than the 
other; but as the Arctic and Scottish specimens appear to 
agree so closely in every other respect, we can meantime 
regard this northern form only as a variety of Parartotrogus 
Richardi. 
* In the original description of Parartotrogus Richardt in the Ann. & 
Mag. Nat. Hist. (6) vol. x1. p. 210, the authors were somewhat uncer- 
tain whether it was the second or the fourth pair that was wanting ; but 
Dr. Giesbrecht of Naples has shown that it is the fourth pair, so that 
the “ ? third and fourth pairs ” in the original description should be the 
“second and third pairs.” 
Ann. & Mag. N. Hist. Ser. 7. Vol. viii. 26 
