NARRATIVE OF THE CRUISE. 
£47 
infer from an examination of them whether it was of marine, estuarine, or inland 
origin. 
The marine Ostracoda of the British Islands consist of at least thirty genera, 
of which twenty-eight are represented in the Challenger collection ; but it must be 
remembered that during the cruise of the Challenger very few collections were made in 
the neighbourhood of the shore, which region usually swarms with these small animals. 
The genus Par ado xo stoma in British seas, is almost exclusively a littoral one, and it is in 
this zone that many members of other genera attain their highest development, and 
there is no doubt that shore-collecting in the tropical and subtropical seas would yield 
rich results to a student of Ostracoda. 
Only two natatory pelagic species have been found by the Challenger to exist 
in all the areas explored, viz., Halocypris atlantica and Halocypris brevirostris. 
These were sometimes captured in great numbers when the tow-net was dragged about 
a c 
Fxo. 315 . — Cythere dictyon, G. S. Brady. 
Male ; A, from the side ; B, from the front ; C, from below. 
Fig. 31(3 . — Krithe prod it da, G. S. Brady. 
A, male, left side ; B, female, from the front; C, male, 
from below. 
50 fathoms beneath the surface. The reason of this wide distribution is sufficiently clear 
if it be remembered that as regards animals living for the most part near the surface of 
the sea, and dependent, probably, upon no restricted or specially localised supplies of 
food, the only impediments to universal distribution are conditions of temperature. So 
far as yet appears, the limit of endurance in these species is reached at about 50° S. 
and 35° N. latitude. 
The species which are most nearly cosmopolitan in their distribution are Cythere 
dictyon (see fig. 315), Cythere dasyderma, and Cythere acanthoderma. This statement, 
however, by no means expresses their ubiquitous distribution in the deep sea, a fact 
which only becomes apparent when it is observed that amongst the forty-five dredgings 
exceeding 100 fathoms at which Ostracoda were taken, Cythere dictyon is noted 
twenty-three times, Cythere dasyderma nineteen times, and Cythere acanthoderma 
seven times. 
One of the most common of deep-sea Ostracoda is Krithe producta (see fig. 31G), 
(narr. chall. exp, — vol. i. — 1885 .) 107 
