506 GEOFFREY SMITH. 
has the biting face divided into three regions—an upper 
toothed portion, which differs slightly in the right and left 
mandible, a lobe bearing a row of spines, and a lower molar 
surface. The lacinia mobilis, characteristic of the Peracarida, 
is absent. The palp is three-jointed. The mandible of 
Paranaspides lacustris (text-fig. 10) has the same 
structure as the above, but the palp has a peculiar formation, 
which is particularly well marked in old specimens. In old 
specimens it appears to be distinctly four-joimted, and the 
basal joint carries a very definite, little, external branch 
TExT-FIG. 10, 
Paranaspides lacustris. Mandible. 
tipped with two sete. In young specimens the extra joint, 
i.e. between segment two and three, may be absent, and the 
external branch is not so conspicuous. The external branch 
occupies the position of an exopodite, and if the mandibular 
palp in this form is really biramous, it would be unparalleled 
in Crustacea except among the Copepoda and Ostracoda. 
Considering, however, that Paranaspides is otherwise a 
rather specialised form, and that the character in question 
is best marked in old specimens, it seems doubtful if we are 
really dealing with a primitive characteristic. 
