PTEKOPODA AND GASTROPODA. 575 



A. Ilolostomato. Margin of the shell-aperturo entire. 

 Family Cupuloidtc. Shell limpet-shaped, with the apex sub- 

 spiral. 



Genera Pihopsis, Hipponyx, Crepidida, CalyptroEa, Lithedaphus. 



Family Turhinidce. In the following families the shell is spirnl 

 and pyramidal, or turbinated. 



Genera Turho, Phasianclla, Troclms, Monodonta, Delphinnla, 

 Euomphalus, Stomatella, Droderipia. 



Family Keritida;. 



Genera Nerita, Pileohis, Neritina, Navicella. 

 Family Paludinidce. 



Genera Paludina, A)npullaria, Valvata, Janthina. 



Family Litorinidce. 



Genera Litori7ia, Solarium, Litiopa, Pissoa. 



Family TurritellidcB. 



Genera Turritella, Vermetus, Scalaria. 



Family Melaniadce. 



Genera Melania, Paludomus, Melanopsis. 



Family CerithiadcB. 



Genera Cerithium, Potamides, Nerincea, Struthiolaria. 



Family Pyramidellida;. 



Genera Pyramidella, Stylina, Macrocheilus. 



Family Naticidce. 



Genera Natica, Sigaretus, Velatina. 



B. Siphonostomata. Margin of the shell-aperture notched or 



produced into a canal. 

 Family Cyprceidce. 



Genera, CyprcBa, Erato, Ovidum. 



Family Volutidce. 



Genera Valuta, Oliva, Cymha, Mitra, Valvaria, Maryinella. 



Family Conidce. 



Genera Conus, Pleurotoma. 



Family Bucci7iidcB. 



Genera Buccinum, Harpa, Cassis, Purpura, Ehurnea, Terebra, 

 Nassa, Monoceros, Dolium. 



Family Muricidce. 



Genera Murex, Ranella, Triton, Fasciolaria, TurhincUa, Can- 

 ceUaria, Pyrula, Fusus. 



Family StrombidcB. 



Genera Stromhus, Pteroceras, liosiellaria. 



