506 . 
W. T. CALMAN. 
which the carapace is entirely absent. It is this that gives 
special importance to the agreement between Batliynella 
and some of the genera of fossil Syncarida (Uronectes, 
Palasocaris) in which the first thoracic somite is similarly 
free from the head. 
YI. The Mandibular Groove in the Syncarida. 
Anaspides was originally stated to have, as Batliynella 
has, eight free thoracic somites, but I pointed out in 1896 
that the supposed first thoracic somite was defined from the 
head not by a movable articulation like those between the 
following somites, but by a superficial groove in the integu- 
ment, and that this groove, from its position immediately 
behind the mandibles, probably did not mark the cephalo- 
thoracic boundary. 1 I later expressed some uncertainty as to 
this interpretation, but it was strongly confirmed by the 
discovery that in the fossil genus Palaeocaris (Text- 
fig. 13, A) where eight free thoracic somites are clearly 
defined, a short groove is present on the side of the head, 
running upwards from the base of the mandible in exactly the 
same position as the more strongly marked groove of Ana- 
spides (Caiman, 1911, p. 489). To this groove, thus shown 
to have nothing to do with the first thoracic somite, the name 
of “ mandibular groove ” (Text-fig. 13, m. gr.) was given, and 
it is of particular interest to find it present also in Bathy- 
nella. In this genus the groove, although no more con- 
spicuous than it is in Koonunga (Text-fig. 14) lias the same 
relative position as, and is undoubtedly homologous with, that 
1 The “ faint impressed line ” described (Caiman, 1896, p. 788) as 
running behind the mandibular groove in Anaspides is very ill- 
defined and inconstant, and no morphological significance can be 
attributed to it. The “ horizontal groove ” is not so deep or so sharply 
marked as the mandibular; it is still shallower in Paranaspides, 
and in Koonunga I can only see a doubtful trace of it. It is asso- 
ciated with a bulging of tfye side wall of the head in this region (shown, 
for instance, in Sayce’s figures of Koonunga), which apparently marks 
the position of the maxillary gland. 
