Several of the marine and many species of freshwater algae are peculiar to the island.
They consist chiefly of sands and clays of aeolian and freshwater origin.
At suitable localities of the coast which are sheltered from the waves and overgrown with seaweed, especially in rock-pools, one or two males establish themselves with their harems, and may be observed without difficulty, being quite as fearless as their freshwater cousins.
Next, proceeding from this region in an easterly direction, are the Neogene freshwater formations, filling up the greatest part of the north-east of Bosnia, as also a zone of flysch intermingled with several strips of eruptive rock.
Other freshwater fish are the perch, black bass, pike, pickerel and white fish.
The very large assemblage of forms coming under this order comprises the most highly developed predaceous sea-snails, numerous vegetarian species, a considerable number of freshwater and some terrestrial forms. The partial dissection of a male specimen of the common periwinkle, Littorina littoralis, drawn in fig.
There are not many varieties of freshwater fish, the commonest being the baba or cat-fish and the yellow fish.
The Pliocene, on the other hand, is of freshwater origin, and contains silicified wood and numerous remains of Mammalia.
Chlorophyceae include both marine and freshwater plants.
Upon these rest patches of freshwater deposits containing numerous remains of plants.