MAEINE MOLLUSCS 



241 



denoting a somewhat closer relationship to the more advanced uni- 

 valves. They have distinct heads, with prolonged muzzles, and 

 well-formed antennae and eyes. The teeth of the lingual ribbon 

 are single, with dentated laterals on either side. 



The Cup-and-saucer Ijimpet^alyptrceasinensis) is so called on 

 account of a curved plate that projects from the interior of the 

 shell, at the apex ; and though this plate takes the form of a half- 

 cup rather than of a cup, the whole shell has suggested the popular 

 name, while the generic name is 

 derived from calyptra, which sig- 

 nifies a cap. This mollusc is occa- 

 sionally found among stones at low 

 tide, but usually lives beyond this 

 line, thus necessitating the use of 

 a dredge. The Bonnet Limpet 

 (Pileopsis hungaricus) is of similar structure and habit, but the 

 nucleus of the shell is a more decided spiral (see Plate V.). Both 

 these animals adhere to stones and rocks, and, like the common 

 limpet, seldom or never move from their selected sites ; hence 

 their shells are variable in form, being adapted to the rock below, 

 and the movements of the shell often cause a little hollow to be 

 scooped out of the softer materials. 



Yet other limpets belong to the next family Fissurellidce, which 

 is characterised by a perforation or a notch in the shell. In these, 

 too, the shell is conical, with a tendency to assume the spiral form, 

 but the curve of the nucleus, which is always apparent in the young 

 shell, frequently disappears as the growth proceeds. 



FIG. 167. Calyptrcea sinensis 



128 



FIG. 168. Fissurellidee 

 1. Puncturella noachina. 2. Emarginula rtticulata. 3. Fissurella reliculala 



In the Keyhole Limpet (Fissurella reticulata) which is found 

 chiefly on our southern shores, the perforation is at the summit 

 of the shell ; but as the animal grows the hole increases in size, 

 encroaching on the curved nucleus until the latter quite disappears. 

 In the genus Puncturella the perforation is just in front of the 



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