of British Entomostraca. 413 
This animal is very small. The shell is rounded on the pos- 
terior margin, bulging out anteriorly, and terminating at infe- 
rior angle ina sharp point or spine, which projects straight down- 
wards. The superior antenne consist of twenty articulations ; the 
seven first are short and close to each other; at the seventh two 
or three setz spring, projecting forwards and upwards ; then fol- 
low thirteen articulations, each one longer than the preceding. 
It requires a strong magnifying power to make out this articu- 
lated structure distinctly. Like the antennules of the Daphnide 
and Lynceide they appear to be almost destitute of motion, and 
thus, when seen close to each other, they certainly bear a close 
resemblance to a prolongation of the beak. The inferior antenne, 
though strong bodies, are much shorter than in most of the 
Daphnide. The anterior branch has four articulations, the pos- 
terior only three. They are furnished with long filaments, which 
are not plumose. ‘The ova are few in number. The motion of 
this curious little creature through the water is caused by nume- 
rous and very rapid strokes of its inferior antenne or rami, being 
in that respect very similar to the Lynceide. The males I have 
never yet met with. 
Section 2. Ostracoda. 
The genus Cypris as established by Miiller has hitherto re- 
mained intact. As however a number of the species which have 
been described possess a set of organs which many others do not, 
and which exercise a decided influence upon their ceconomy and 
habits, I think it becomes incumbent upon us to separate the 
two sets of species into distinct genera. In the one set the ani- 
mals have a much greater degree of motion and agility than the 
others, swimming freely and rapidly through the water in all di- 
rections, and apparently possessing a higher degree of enjoyment 
in their existence. This arises from a bundle of long plumose 
sete which spring from the second articulation of the pediform 
antennze (the first pair of feet of Miiller and others), and by 
means of which they can suspend themselves in the water or 
transport themselves through it with great facility. The other 
set are deficient in this apparatus, and instead of swimming gail 
through the limpid element, crawl in the mud at the bottom of 
the pools in which they are found, or creep along the aquatic 
plants which grow there, and if dropped into a glass of water fall 
to the bottom without being able to suspend themselves for the 
shortest time. They thus form a connecting link between the 
genera Cypris and Cythere. | 
I propose characterizing them thus :— 
Gen. 1. Cypris, Miiller. 
Two pairs of feet, one pair always contained within the shell. 
