GASTEROPODA. 153 



Shell conical ; apex posterior, spirally recurved ; aperture rounded ; mus- 

 cular impression horse-shoe shaped. 



Animal with a fringed mantle-margin ; lingual teeth like catyptrcea. 



P. hungaricus (the Hungarian-bonnet) is found on oysters, in 5 to 15 

 fms. water; more rarely as deep as 80 fms., and then very small. P. mili- 

 taris is extremely like a velutina. 



Distr., 7 sp, W. Indies, Norway, Brit., Medit., India, Australia, Cali- 

 fornia. 



Fossil, 20 sp. Lias . Europe. 



Sub-genus. Amathina, Gray. A. tricarinata, PL XI., fig. 19. Shell 

 depressed, oblong ; apex posterior, not spiral, with three strong ribs diverging 

 from it to the anterior margin. 



Platyceras, Conrad (acroculia, Phil.). P. vetustus. Garb., limestone. 

 Brit. 



Fossil, 20 sp. Devonian Trias. America, Europe. 



HIPPONYX, Defrance. 



Etym., hippos, a horse, and onyx, a hoof. 



Type, H. cornucopia, PL XI., figs. 20, 21. 



Shell thick, obliquely conical, apex posterior ; base shelly, with a horse- 

 shoe-shaped impression, corresponding to that of the adductor muscle. 



Distr., 10 sp. W. Indies. Persian Gulf, Philippines, Australia, Pacific, 

 W. America. 



Fossil, 10 sp. U. chalk . Brit., France, N. America. 



Sub-genus. Amalthea, Schum. A. conica. Like hipponyx, but forming 

 no shelly base ; surface of attachment worn and marked with a crescent- 

 shaped impression. Often occurs on living shells, such as the large turbines, 

 and turbinellee of the Eastern seas. 



FAMILY XIII. PATELLID.E. Limpets. 



Shell conical, with the apex turned forwards ; muscular impression horse- 

 shoe-shaped, open in front. 



Animal with a distinct head, furnished with tentacles, bearing eyes at 

 their outer bases ; foot as large as the margin of the shell ; mantle plain or 

 fringed. Respiratory organ in the form of one or two branchial plumes, 

 lodged in a cervical cavity ; or of a series of lamellae surrounding the animal, 

 between its foot and mantle. Mouth armed with horny jaws, and a long 

 ribbon-like tongue, furnished with numerous teeth, each consisting of a pel- 

 lucid base and an opaque hooked apex. 



The order cyclo-branchiata of Cuvier included the chitons and the limpets, 

 and was characterised by the circular arrangement of the brarichise. At a 

 comparatively recent period it was ascertained that some of the patellse 

 (acmcea) had a free, cervical gill; whilst the chitons exhibited too many 

 peculiarities to admit of being associated so closely with them. Professor 



