LECTURES ON MOLLUSCA. 51 



In Galerus, we have simply a spiral plate running round inside a 

 conical shell. In the "cup and saucer limpets," (Crucibulum,) the 

 conical shell has a cup-like process within, more or less attached to the 

 side of the saucer. In Crepidula, the cone is flattened into a hoat, and 

 the cup into a deck, producing the "Slipper-limpet." In all these 

 forms, which (though differing in the types) are closely connected by 

 intermediate shapes, the animal presents the same appearance. There 

 is a small flat foot, and a little head, with eyes on slender tentacles, 

 and a short muzzle with lips. The mantle scarcely extends to the 

 edge of the shell. The tongue is armed with teeth, as ferocious as 

 those of Natica and Cassis, and yet they seldom walk about, adapting 

 themselves to the shape of the object to which they adhere, and growing 

 very finely under circumstances in which locomotion is impossible. 

 Ind'eed, in the genus Calyptrcea, in which the "cup" is cut across, 

 the animal exudes a shelly support from its foot, by which it is abso- 

 lutely cemented to the rock. The remarkable changes of form which 

 these creatures assume according to the circumstances of their growth, 

 were detailed in the Smithsonian report for 1859, pp. 197-205. In 

 their early stage however they are very similar ; having a regular, spiral, 

 globular shell, from the pillar of which the deck or cup is afterwards 

 developed. 



Family CAPULID^E. (Bonnet Limpets.) 



The animals in this family closely resemble the Slipper-limpets, but 

 the adductor muscle is not fixed to any shelly support in the form of 

 cup or deck. The shell is simply an irregular cone, twisted more or 

 less into a spiral at the apex. Some of the living species of Capulus 

 greatly resemble the Velutinas in form ; but they are heavier shells. 

 The AmaUheea eats a deep hole into the shells on which it rests, with 

 a horseshoe ridge in the centre. Hipponyx deposits so thick a shelly 

 layer under its foot (like Calyptrcea) that the fossil species were long 

 thought to be bivalve shells. The horseshoe muscular scar, formed 

 by the attachment of the adductor, is very conspicuous in this family. 

 It equally exists however in the spiral shells. 



Even in the Palaeozoic rocks appear forms which cannot be dis- 

 tinguished from the members of this family. They have been described 

 as Metoptoma, Platyceras, Acroculia, &c. 



Family NARICID^I. 



The Naricce are a group of shells, looking like cancellated Natica, but 

 made by a very different animal. They are, as it were, Bonnet-limpets 

 rolled into a true spiral shell. Their habits are sluggish, but they move 

 about somewhat, and are provided with a very thin, sub-spiral oper- 

 culum. As in the last families, the creatures are ovoviviparous, 

 keeping their eggs under a fold in the mantle till they are ready to 

 hatch. The shells were first called Vanicoro by the French naturalists, 

 but it is scarcely fair to call a race of creatures by the proper name of 

 a place. It is probable that the curious shells called Neritopsis, with a 

 scooped out pillar lip, belong to this family. Only one species is now 

 living, but many are found fossil in the newer rocks. Without a 



