190 ON THE ANATOMY AND AFFINITIES OF 
of the antenna, and the inner of the two endognaths. On the left 
side, its well-marked curved boundary is distinguishable between the 
antenna and the broken edge of the stone. 
Towards the junction of the middle and anterior thirds of the left 
lateral edge, a long, flattened, filiform appendage (c) comes off from 
the carapace. On the right side, the remains of two such appen- 
dages, with, perhaps, traces of a third, are visible (7). They come 
off close to the two endognaths, and one might be inclined to suppose 
them all, organically connected with the latter, were it not for the 
independent appendage on the opposite side. 
In the other, smaller, half of the specimen the only points to be 
noted are, the greater distinctness of the right boundary of the 
“sculptured area” in front of the carapace, and of the right (here left) 
filiform appendages. I am strongly inclined to think that the 
“sculptured area” in this fossil is the epistoma. The interpretation 
of the filiform impressions is more difficult. That on the left side 
seems to be attached directly to the carapace, and in that case might 
be a second antenna. If this be its nature, the impressions on the 
other side may be the corresponding appendage and the palps of the 
endognaths. On the other hand, it must be remembered that there 
is no independent evidence of the existence of a second antenna in 
the genus, and that the position of the filiform appendage on the left 
side may be purely accidental. 
4. The two singular fossils figured in Plates XII. [Plate 23] 
fig. 16, and Plate XIII. [Plate 24] fig. 16, are the only remains, 
which, from their sculpture, may be, with every probability, referred 
to Prerygotus, but which are not as yet referable to their proper place 
in the organization. 
These parts present, at first sight, a striking resemblance to the 
terminal palette of an ectognath, with a portion of the penultimate 
articulation. They are described at length in the systematic portion 
of this Monograph (p. 255); and I will, therefore, only remark in 
this place that, as the ectognaths of P prodblematicus and arcuatus 
(the species to which these remains probably belong) have not yet 
been observed, it is possible that they may be their distal joints. 
Pending sufficient proof that such is the case, however, it must be 
borne in mind that they differ in several important respects from any 
ultimate and penultimate joints of an ectognath at present known. 
The only alternative which suggests itself is that these parts may 
have been thoracic or abdominal appendages. 
5. The fossil figured in Plate XIIL.. [Plate 24] fig. 17, is evi- 
dently crustacean, but it exhibits no character by which it can be 
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