" SHELLS " 309 



may sometimes be found at spring tides at extreme tide limit. Its shell is 

 ridged from the peak to the margin, and at the top is a hole shaped like a key- 

 hole. Through this the water, passing over the gills, is squirted out by the 

 mollusc. 



13. The Smooth Limpet (Patella pellucida) is much smaller than the common 

 species, and has a thin delicate shell, pale brown, with eight or nine narrow 

 blue lines running down it. It will be found at extreme low-tide limit, where 

 it feeds on the Great Oar-weed. 



14. The Cup-and-Saucer Limpet is a South Coast mollusc, to be identified 

 by its internal appearance. Inside the shell is a curved plate like a cup, the 

 shell itself forming the saucer. To make it complete, at the end of its tooth- 

 ribbon is an organ like a teaspoon ! 



15. The Painted Top (Trochus magus). One of a number of cone-shaped 

 shells, coming to a sharp point, usually beautifully coloured. This species 

 has many streaks, dots, and patches of scarlet, pink, blue, white, and other 

 colours, though the colouring is often damaged. The ridges of the shell 

 are bold and plain. It is, like the rest, a vegetable feeder. All have 

 opercula. 



16. The Grey Top (T. cinereus) is smaller, yellowish grey, with dark zigzag 

 marks. 



17. The Common Top (T. zizyphinus) is not so plentiful, but may be identi- 

 fied by its reddish zigzag lines. 



18. The Chiton, or MAIL SHELL (Chiton cinereus), has a remarkable shell, not 

 unlike in appearance that of a tortoise. It consists of a number of plates 

 (eight altogether), slightly overlapping, and, like the Wood-louse, it can roll 

 itself up into a ball. It is ashy grey and is found on rocks. Length about 

 \ inch. 



19. The Bristly Mail Shell (C. fascicularis) has small bunches of bristles 

 along the shell border opposite each plate. 



20. The Smooth Mail Shell (C. Icevis) is known by its reddish colour and 

 glossy smoothness, and by the possession of a central ridge. 



21. The Marbled Mail Shell (C. marmoreus) is the largest of the Chitons 

 (i-ij inch). The colour is a general marbling of brown and yellow. 



22. The Necklace Natica (Natica monilifera) is a very familiar species, 

 rounded, smooth, and glossy (having an operculum), with three lines of arrow- 

 heads upon it. It gets its English name from its eggs, which are glued together 

 into a broad spiral band not unlike a necklace. When alive, the mantle nearly 

 covers the shell. 



23. The Turret Shell (Turitella communis) is spiral in form, with ridges 

 running from apex to mouth. It is fairly large. 



24. The Ruddy Pyramid (Chemnitsia rufescens) is smaller, and the ridges 

 run crosswise instead of down. 



25. The Horn Shell (Cerithium reticulatum) is spiral also, and marked by 

 rows of regular dots. 



