142 THE SEA. 



whelk belongs to the series. Thus one of the humblest of our shell-fish is allied to the 

 animal from which a nearly priceless dye was once obtained. 



The genus Hnrpa includes some beautifully marked and coloured shells, of which 11. 

 ventricosa is an attractive example. These are chiefly found in the Indian Ocean. The 

 Rock Shells (Mttre.r) abound in every sea, but are finer and more branching in the 

 warmer ones. They are remarkable for bright colours and fantastic forms. The shell is 

 oblong with a long spire attached, its surface often covered with rows of branching 

 spines. The genus Triton, of which about one hundred species are known, is 

 ranged with the genus Murex, on account of points of similarity. The Marine Trumpet 

 (Triton varlegatnm) which sometimes attains a length of sixteen inches, is a fine example. 

 The genus Stromlus includes among its species the great roughly ornamental shells, 

 often used for grottoes or rockeries. Some of the streets of Yera Cruz are said to be 

 paved with them. Oddest and most remarkable of all the marine shells to be found in the 

 naturalist's collection are those of the genus Pteroceras. They are of fresh and brilliantly 

 shaded colours. 



And now to the Pteropocla, practically " winged feet " molluscs, the position of which 

 in scientific nomenclature many think unsatisfactory. This is, however, of little consequence 

 to the general reader. These curious little molluscs can pass through the deep blue seas 

 they usually inhabit rapidly, reminding us strongly of the movements of a butterfly or 

 some other winged insect. They can "ascend to the surface very suddenly, turn them- 

 selves in a determinate space, or rather swim without appearing to change their place, 

 while sustaining themselves at the same height." " If/' continues Figuier, " anything 

 alarms them, they fold up their flappers and descend to such a depth in their watery world 

 as will give them the security they seek. Thus they pass their lives in the open sea far 

 from any other shelter except that yielded by the gulf weed and other algse. In appear- 

 ance and habits these small and sometimes microscopic creatures resemble the fry of some 

 other forms of mollusca. They literally swarm both in tropical and arctic seas; and 

 are sometimes so numerous as to colour the ocean for leagues. They are the principal food 

 of whales and sea-birds in high latitudes, rarely approaching the coast. Only one or two- 

 species have been accidentally taken on our shores, and those evidently driven thither 

 by currents into which they have been entangled, or by tempests which have stirred the 

 waters with a power beyond theirs. Dr. Leach states that in 1811, during a tour to 

 the Orkneys, he observed on the rocks of the Isle of Staffa several mutilated specimens of 

 Clio lorealis. Some days after, having borrowed a lai-ge shrimp net, and rowing along the 

 coast of Mull, when the sea, which had been extremely stormy, had become calm, he 

 succeeded in catching one alive, which is now in the British Museum." Professor Huxley 

 has told us that they have auditory organs, are sensible of light and heat, and probably 

 of odours, but that they possess very imperfect eyes and tentacles. They have respira- 

 tory organs, hearts and livers, and are undeniably social and gregarious, swarming 

 together in great numbers. 



We now approach the highest class of the mollusca on paper, only, be it observed, 

 for in actual life most of them are either nearly unapproachable, or, at all events, are most 

 undesirable acquaintances. 



