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 in a sharp point or spine, which projects straight down- 

 wards. The superior antennse consist of twenty articulations ; the 

 seven first are short and close to each other ; at the seventh two 

 or three setse 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 DaphnidcB 

 and LynceidcB 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 antennse, 

 though strong bodies, are much shorter than in most of the 

 Daphnidce. 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 antennse or rami, being 

 in that respect very similar to the Lynceidce. 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 oeconomy 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 

 setse which spring from the second articulation of the pediform 

 antennse (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 gaily 

 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. 



