GASTEEOPODA. 153 



Shell conical ; apex posterior, spirally rcciu-ved ; aperture rounded ; mus- 

 cular impression horse-shoe shaped. 



Animal with a fringed mantle-margin ; lingual teeth like cali/ptrcea. 



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. 



Bistr., 7 sp, W. Indies, Norway, Brit., Mcdit., India, Australia, Cali- 

 foruia. 



Fossil, 20 sp. Lias — . Eiu'ope. 



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

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

 from it to the anterior margin. 



Plati/cera-s, Conrad (acroculia, Phil.). P. vetustus. Carb., limestone. 

 Brit. 



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



HiPPONYX, Defrance. 



Etpn., hi/ppos, a horse, and onyx, a hoof. 



Type, H. cornucopia, PI. XL, figs. 20, 21. 



Shell thick, obliquely conical, apex posterior ; base sheUy, wdth a horse- 

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



Bistr., 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 sheUy base ; surface of attachment worn and marked with a crescent- 

 shaped impression. Often occm-s on lining shells, such as the large tiu-bines, 

 and tiu'binellse of the Eastern seas. 



FAjMILY XIII. Patellid^. Limpets. 



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

 shoe-shaped, open in front. 



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

 their outer bases-; foot as large as the margin of the sheU ; 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 lameUso surrounding the animal, 

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

 ribbon-like tongue, fm-nishcd 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 branchiae. At a 

 comparatively recent period it was ascertained that some of the patellee 

 [acmaa) had a free, cervical giU ; whilst the chitons exhibited too many 

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



