Land and Fresh-Water Crustacea around Edinburgh. 47 
small collection of Ostracoda, and of drawing attention to a 
few of the more interesting species that had been obtained 
within the Edinburgh district; the aim of the present com- 
munication is to put on record all the species—common as 
well as rare—that are known to occur within the prescribed 
area. But, before proceeding to give an enumeration of the 
species, it may be desirable to offer a few remarks upon the 
distribution of the Ostracoda. 
Speaking generally, the Ostracoda are to be found almost 
everywhere where there are pools of water. Some of them 
are more commonly found in water of questionable purity, 
such as may be seen stagnant in ditches and marshy 
ground, and possessing an odour of a rather disagreeable 
kind; but, while that is the case, I do not remember having 
ever observed Ostracoda in water that was largely mixed 
with sewage,—the impurity of the water in which such species 
are found is usually the result of the decay of vegetable 
matter in the bottom or round the sides of the pool, or loch. 
It may be also stated, as a rule, that all the species are more 
or less confined to still water, as that of ponds, lochs, canals, 
etc., and are rarely obtained in running water. There are 
some curious and interesting problems, relating to the laws of 
distribution of species, presented by the Ostracoda—in one 
locality a single species may be found in the greatest abund- 
ance to the exclusion of almost every other form, while in 
another locality, where the conditions appear to be equally 
favourable, that species may be very scarce or entirely 
absent. To bring out this more clearly, I may relate my 
experience of a single species, viz., Cypris incongruens. In 
Garvel Park, Greenock, previous to the construction of the 
James Watt Dock, there were some pools of water, and, 
during May 1880, the weather being dry and warm, one of 
these pools dried up. There had been a good deal of con- 
ferva in the pool, and this, when the water disappeared, 
formed a substance, almost like felt, covering the bottom. 
On removing some of this felt-like material, Cypris incon- 
gruens was observed in myriads, and, so far as I remember, 
was the only Ostracod present. During the autumn of 1888 
I happened to be several times in the neighbourhood of 
