536 MOLLUSCA 



Division 2. T^NIOGLOSSA. 



Shell very variable in shape, with or without siphonal canal; 

 radula (Fig. 830) long and narrow, with 1 central, on each side of 

 which are 1 lateral and 2 marginal teeth, making 7 in each row : about 50 

 families, grouped in 2 subdivisions, including most prosobranchs. 



Key to the subdivisions of Tcenioglossa: 



Ui Foot with a broad sole 1. Platypoda 



c. Foot fin-shaped ; animals pelagic 2. Heteeopoda 



Subdivision 1. PLATYPODA. 



Shell well developed; foot with a broad sole, with which the animals 

 creep: 48 families, marine and in fresh water. 



Key to the families of Platypoda here described ; 



Ci Aperture rounded, without siphonal canal (Fig. 831, 2). 

 6i Animals marine. 

 Ci Shell regularly coiled or much flattened, 

 di Shell not long and slender, but more or less globose or flattened. 

 Ci Shell conical and with a distinct spire (Fig. 772,3). 

 /i Umbilicus open (Fig. 831, 1) or more or less closed by a large callus. 



1. Naticidae 



fj Umbilicus closed 3. Littobinidae 



ea Shell either not spiral or much flattened. 



/i Spiral either absent or very inconspicuous 2. Capulidae 



/j Shell spiral, but discoid 6. Skeneidae 



^2 Shell elongate with a high spire. 



Ci Shell minute, less than 5 mm. long, with 5 or 6 whorls 4. Rissoidae 



€2 Shell very long, with about 10 whorls 12. Turritellida.e 



Cj Shell with a very irregular spiral 13. Veemetidae 



62 Animals in fresh water. 

 Ci Shell usually minute, less than 5 mm. long, and always less than 10 mm. 



di Shell usually elongate and conical 5. Hydrobiidae 



di Shell usually flattened and discoid 8. Valvatidae 



Cg Shell not small, usually much more than 12 mm. long ; heliciform 

 (Fig. 772). 



di Snout simple ; tentacles short 7. ViVlPABiDAE 



di Snout divided into 2 long tentacular lobes ; tentacles long. 



9. Ampullabiidae 

 o. Aperture elongate, with siphonal canal (Fig. 872, 1). 

 61 Canal short (Fig. 854), sometimes consisting only of the narrowed lower 

 edge of the aperture. 



Ci Surface ridged or tuberculated 10. Ceeithiidae 



Cj Surface usually smooth 11. Pleurocebidae 



6j Canal long; aperture usually long and narrow (Fig. 859). 

 Ci Spire low or hidden ; aperture nearly as long as the shell. 



di Spire almost or entirely hidden 15. Cypileidae 



d. Spire free and raised. 

 Ci Shell thick, with thick reflexed lips. 



/i Outer lip with a notch near the lower end 14. Strombidae 



/a Outer lip without a notch 17. Cassididae 



€2 Shell thin, with a thin lip 16. Doliidae 



c. Spire high ; aperture not half as long as shell 18. Tritonidae 



