bo 
Or 
support large parasites, whereas large species like Calliopius leviusculus Ky., Munnopsis 
typica M. Sars and Hippolyte, are inhabited by large animals. 
In most species the regular, rounded, ovate or globular shape of the body is inter- 
rupted in front or a little behind the anterior margin on the ventral side by a small pro- 
truding head, which as a rule is tolerably well defined at the basis. In the adults it 
is most frequently very small, compared with the trunk; in small, and_ particularly in 
recently hatched specimens (pl. VII, fig. 2e, and especially pl. III, fig. 2c) it is of a very con- 
siderable size. The reason of this difference is that the head and its organs do not grow or 
at most grow very little, whereas the trunk greatly increases in size, in order to give room 
for the mighty production of eggs. In some forms there is no separate head at all, so that 
its (very small) organs: antennule, antenne, mouth, maxillule, maxilla and maxillipeds, are 
situated near each other anteriorly on the ventral side of the vaulted body. In Stenothocheres 
(pl. I) the thorax has two rather small pairs of limbs; in the other genera these limbs are quite 
minute or wanting altogether. In Stenothocheres we find a distinctly marked, prominent 
abdomen. — In no species the body shows any vestige of segmentation. 
This will give a general idea of the females. In giving a closer description of their 
structure I think the best plan is to begin with Spheronella and kindred forms, as the 
genus Stenothocheres, though in two important points — the size and development of the 
trunk-legs and the existence of an abdomen — more closely related to less transformed Cope- 
poda, in other respects is less qualified for serving as base of the description. 
I. Homocoscelis, Spheronella and Choniostoma. Many species have a prominent, 
well defined head: the back, front part and sides are evenly vaulted and pretty well chiti- 
nised, and the chitinous border to the front and on the sides stands out a little beyond the 
ventral side, which is partly covered by a soft membrane, and has a somewhat concave 
surface. Seen from below, the sides of the head are arched posteriorly, for the above- 
mentioned protruding lateral borders are somewhat removed from the outline of the head; 
they are generally ciliated, whereas the margin of the frontal border is mostly hairless. As 
a rule, a narrow, arched, transversal list, or two narrow, parallel lists, proceeding from the 
posterior ends of the lateral margins and passing behind the basis of the maxillipeds, forms 
or form the posterior limit of the head. Sometimes this list is interrupted at the median 
line (pl. IIT, fig. 2c), sometimes it does not reach the lateral margins (pl. VIII, fig. 1d). 
Choniostoma (pl. XI) at first sight seems to have no distinct head at all, however, 
the above-described borders in front, posteriorly and on each side remain, forming a frame 
round the soft area, in the middle of which the mouth and its appendages are situated. 
The front part of this frame in Chon. Hansenii (pl. XI, fig. 2d) rises a little beyond its sur- 
roundings, thus representing the only remaining part of the anterior and upper surface of 
the head. 
Spher. Acanthozonis (pl. VII, fig. 5a and 5b) presents a fine intermediate form 
between Choniostoma Hansenii and the species that have a well defined, prominent head 
4 
