496 MOLLUSC A 



SUBORDER 1. TECTIBRANCHIATA. 



Shell and mantle usually present; ctenidium 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 Tectibranchiata here described: 



ctj With well-developed shell, sometimes internal 1. BULLOIDEA 



a, 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 : 



G! Animals not pelagic ; no swimming fins. 



&! Shell external, with a prominent spire. 1. ACTEONIDAE 



6 2 Spire very low or sunken. 

 Cj Shell external. 



di Radula absent 2. TOBNATINIDAE 



d 2 Radula present. 



e x Cephalic disc not bifurcate .3. SCAPHANDBIDAE 



e a Cephalic disc bifurcate 4. AKERIDAE 



c a Shell internal 5. PHILINIDAE 



o a Animals pelagic, with large swimming fins (pteropods). 



61 Shell spiral, sinistral 6. LIMACINIDAE 



6 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; pleuro visceral 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. 7gg inner lip with a strong tortuous fold; animal white; 



to8t?iatlT' len g th 6 mm - : Ca P e Cod to Florida, in 2 to 60 

 (Verrill). 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. BETTTSA Brown. Shell with a slightly raised or flat spire; aper- 

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



