184 UNIVALVES PATELLA. 



most deserving uotice are the P. testudinaria, which 

 has g-enerally its interior of a silvery hue; the P. 

 areolata, P. flammea, and P. compressa, the latter being 

 remarkable for its narrow and lengthened form. 



The shells of a compressed form, and having their 

 margins angularly or irregularly toothed, constitute the 

 second division ; such are the P. saccharina, P. gra- 

 nulans, P. granatina, and P. sanguinolenta. The P. 

 vulgata is the Common Limpet, so abundantly found 

 on the British and European shores. 



The third division includes those species which, on 

 account of the perforation in the summit, are usually 

 called Key-hole Limpets. The principal are the P. 

 graeca, P. nimbosa, P. caffra, P. picta, P. perforata, and 

 P. macroschisma. 



The next division comprehends those species which 

 have the summit pointed and recurved: the P. un- 

 garica, the most remarkable, is a beautiful shell, and, 

 from its similarity of shape, called the Fool's-cap :__ 

 the exterior is usually of a pale fawn color, and the 

 outer margin is bordered with a fringed epidermis; 

 when the interior is of a very bright pink color, this Lim- 

 pet is considered more valuable. The P. lutea has 

 some resemblance to an Haliotis, but the flatness and 

 ear-shaped form of the latter genus, is a sufficient dis- 

 tinction. 



The shells of the fifth division have a marginated fis- 

 sure, which is most conspicuous in the P. fissura. 



The curious internal appendage which characterizes 

 the shells of the sixth division, is strikingly observ- 



