92 H. J. HANSEN. 
of the epistome encompasses the anterior half of labrum. In 
several genera the anterior part of the epistome protrudes as 
a plate or a process in front of the margin of the head. The 
epistome is generally well marked off from the front mesial 
triangular end of the upper surface of the head, but in 
Ancinus (M.-Edw.) both are completely fused. 
The peduncle of the antennule is always three-jointed ; the 
two proximal joints afford sometimes generic differences. 
Flagellum of antennule and antenne show differences of 
minor importance. The mouth-parts are rather reduced in 
Plakarthriine (see the diagnosis of this sub-family); in all 
other forms they are well developed. In the small section 
Ancinini the mandibles are without molar process; in Lim- 
noria besides lacinia mobilis is at most rudimentary ; in all 
other genera both lacinia mobilis and the molar process are 
well developed, but lesser differences are observed. Maxillulee 
and maxille are uniform; the maxillipeds vary much in 
relative length and breadth of second and following joints, 
and in length of the lobes frequently proceeding from fourth, 
fifth and sixth joints. But excepting the few genera men- 
tioned the mouth-parts in this rich family are so uniform that 
descriptions of their shape in various genera are nearly 
worthless if not accompanied with numerous figures. The 
most important features are mentioned below in the diagnosis 
of the family, the sub-families, the section Ancinini, and 
the genus Hemispheroma. ‘The metamorphosis of the 
mouth-parts in the females of several genera is treated in 
Chapter III. 
The thorax.—It is a feature probably unique among 
Isopoda that in Plakarthrium the so-called epimera are 
developed as movable plates not only on the six posterior 
segments—which also is the case in Limnoria—but even on 
the first segment. The fusion of these plate-shaped joints of 
the legs with their segment in the Spheromine needs no 
special mention. 
In most genera the legs are uniform as to main points; 
the seven pairs of the same animal and the corresponding 
