50 LECTURES ON MOLLUSCA. 



the Strombs, they all make their shells with a wide rim ; but they 

 have the propensity to stick pieces of stone and broken shell to their 

 backs, so as often to hide what they have made themselves. By this 

 means they probably escape detection. In Pliorus, the pillar is solid, 

 and the operculum thin, concentric, with the nucleus at the side. In 

 Onustus, the pillar is open, and the layers of the triangular operculum 

 are piled one upon another. 



Family APORRHAI'DJE. (Spout Shells.) 



These creatures may be regarded as Spindle-strombs, passing back 

 to the ordinary type, with the common eyes and crawling foot. The 

 wing of the shell is always enormously dilated, and often clawed ; but 

 no mark has yet been found out by which the numerous fossils of the 

 secondary rocks can be referred to one or to the other group. The two 

 British species, A. pes-pelicani and A. pes-carbonis have, as their name 

 implies, very wide claws. The New England species has a broad palm 

 without fingers. The breathing canal in all the members of this family 

 is simply a fold in the mantle entirely covered by the shell. The 

 operculum is like that of the Whelks, but the animal is widely different. 

 The Struthiolarice have a simple varix instead of a wide lip. They are 

 peculiar to the Australian seas. A very curioiis shell, Halia, like a 

 marine Achatina, has been referred to this group ; as also has TricJio- 

 tropis; but we must wait for a knowledge of their anatomy. 



Family PEDICUL ARIADNE. 



The Pedicularia is a curious little shell, living as a parasite on coral 

 in the Mediterranean. When young it is spiral, when adult flat and 

 open like Concholepas. The most singular point about it is the den- 

 tition, which is like that of Strorribus and Aporrhais exaggerated. The 

 outside teeth are produced into enormous claws, like the fingers of a 

 bat's wing folded together. In this respect it resembles Carinaria. 

 This and the following families are of sedentary habits, either crawling 

 about in crypts and chinks, or remaining absolutely fixed for life. 

 They are very degraded animals, as compared with the noble Strombs ; 

 yet their dentition is more allied to them than to the Periwinkles. 

 The fixed shells must of course live on what the water vouchsafes to 

 bring them ; why therefore their tongues should be armed with weapons 

 of war it is difficult to say, as the bivalves, which live in the same 

 way, are entirely destitute of them. How much our ignorance is 

 revealed to us by the little knowledge which we possess ! 



Family CALYPTILEIDJE. 



The Slipper-limpets and their allies have the gills in long, slender 

 plates, forming an oblique line across the cavity. They may be de- 

 scribed as Carrier Shells, which have become tired of a jumping life, 

 and have gone into retirement. In shape of shell, Trochita has a very 

 close resemblance to PJiorus. But instead of a leaping foot, retractile 

 into the shell, and closed with operculum, its foot occupies the base of 

 the "top;" and the operculum is the rock or shell to which it adheres. 



