Fig. 231. Monodonta Australis (Lamarck). Fig. 232. Monodonta labia (Lamarck).
The eighth family is Neritidæ, of which we give as types, Pileolus and Nerita. The hoof-shells, or Nerites, are numerous and pretty, and in external form approach Turbo.
Fig. 233. Delphinula sphærula (Kiener).
Of the Delphinula only a small number of living species are known. They are natives of the Indian Ocean, and remarkable for their numerous spines and the asperity of their shell (Fig. 233).
The ninth family, Paludinidæ, contains Ampullaria, the idol snail of India, and the widely distributed Paludina.
Our tenth family, Littorinidæ, contains Solarium, and the periwinkles, Littorina and Phorus, example, P. Conchyliophorus (Fig. 224).
The genus Imperator belongs to the Turbinidæ, and as examples of it we may instance the Spurred Trochus, Imperator stella, which is studded with radiating spines (Fig. 234), and Imperator stellaris (Fig. 235); they are natives of the Australian seas. Imperator imperialis, vulgarly called the Royal Spur, and Trochus or Rotella Zealandica (Fig. 230), the New Zealand Spur, the spiral turns of which are sculptured in descending furrows, and studded with imbricated scales, which form a projecting edging round the margin of the shell, and give it a radiating form. This species is of a violet brown above and white below, and is still rare in collections.