184 ON THE ANATOMY AND AFFINITIES OF 
those which beset the edge of the basal joint of the appendage () in 
that species. 
That the impressions in question are in fact the remains of 
appendages similar to (6) and (c) becomes a matter of certainty when 
we examine such specimens as those figured on Plate I. [Plate 12] 
figs. 3, 4, 8, 9. 
In fig. 8 is represented an organ, certainly belonging to P. bzlobus, 
whose basal articulation has as nearly as possible the same form as 
that of the appendage (c), and presents, along its free edge, the same 
continuous serration and posterior rounded lobe. The like resem- 
blance is traceable in the joints of the palp-like appendage, except 
that in this specimen a structure was observable, not visible in any 
other, whether of the same or of different species. This is a long 
taper filament, nearly as long as the ultimate and penultimate joints, 
lying on their surface, and apparently attached by its thicker end to 
the distal extremity of the antepenultimate articulation. There are 
indications that this filament was itself jointed. In figs. 3, 4, 9, 
the whole appendage, or at any rate its basal joint, is seen zz széz, 
and on comparing the serrated edge of any of these with the outer 
linear impression first described, the source of the latter will be 
obvious. 
The base of this great limb is attached to the hinder part of the 
carapace; it therefore, without doubt, lay behind the mouth, and 
as it is the outermost pair of buccal appendages, it will be useful to 
call it the “ectognath,” a term more convenient than ‘* maxilla,” 
“ maxillipede,” or “ swimming-foot,” as it involves neither a morpho- 
logical nor a physiological hypothesis. 
The organ which caused the shorter linear impression, lying 
internal to and in front of, that of the cutting edge of the ectognath 
is, I doubt not, similar to that which lies detached in two speci- 
mens, and is figured in the wood-cut, p. 207. It is unfortunately 
impossible in either of these examples to trace, as distinctly as might 
be wished, the precise form of this appendage, but enough is visible 
to satisfy me that this species was provided with one, if not two, 
organs on each side similar in general structure to the appendage (0) 
of P. anglicus, and quite competent to produce the impression in 
question. 
From its general character I entertain very little doubt that the 
appendage (0) is the homologue of the mandible of other Crustacea, 
but as there is some reason to suspect the existence of a third buccal 
appendage, and as it is impossible as yet, supposing this third jaw 
to exist, to say whether any given appendage similar to 4, was first 
