496 MOLLUSCA 



Suborder 1. TECTIBRANCHIATA. 



Shell and mantle usually present; cteuidium usually present and on 

 the right side (Fig. 760, 1) : about 1,400 species, grouped in 3 divisions 

 and 25 families. 



Key to the divisions of Tectihranchiata here described: 



Qi With well-developed shell, sometimes internal 1. Bulloidea 



Cj Shell reduced or absent 2. Aplysioidea 



Division 1. BULLOIDEA. 



Shell either external or internal and well developed; head with a 

 broad dorsal disc, under which the tentacles, when present, are con- 

 cealed; epipodia usually present: 15 families. 



Key to the families of Bulloidea here described : 



Ci Animals not pelagic ; no swimming fins. 



6i Shell external, with a prominent spire '. . . . .1. Acteonidae 



hi Spire very low or sunken. 

 Ci Shell external. 



di Radula absent 2. Tornatinidae 



dj Radula present. 



Cj, Cephalic disc not bifurcate 3. Scaphandridae 



Ca Cephalic disc bifurcate 4. Akeridae 



Ca Shell internal 5. Philinidae 



Oj Animals pelagic, with large swimming fins (pteropods). 



&i Shell spiral, sinistral 6. Limacinidae 



&2 Shell symmetrical and not spiral 7. Cavoliniidae 



Family 1. ACTEONIDAE. 



Shell external, with a prominent spire; epipodia absent, cephalic 

 disc divided behind; operculum horny; pleurovisceral nerve connectives 

 streptoneurous : 7 genera, mostly in warmer seas. 



ACTEON Montfort. Shell solid, ovate; aperture nar- 

 row and one-half the length of the shell: 35 species. 



A. punctostriatus (Adams) (Fig. 755). Shell conical, 

 with 2 or 3 color bands; aperture long and narrow; 

 p. ^g_ inner lip with a strong tortuous fold; animal white; 



Acteonpunc length 6 mm.: Cape Cod to Florida, in 2 to 60 



tostriatus ® ^ ' 



(VerriU). fathoms. 



Family 2. TORNATINIDAE. 



Small external, more or less cylindrical, with the spire sunken or 

 short and elevated; head triangular or quadrangular; tentacles broad, 

 united at the base; eyes distinct; radula and epipodia absent: 3 genera 

 and 120 species. 



1. Retusa Brown. Shell with a slightly raised or flat spire; aper- 

 ture nearly as long as shell, narrow above and dilated below: 50 species. 



