430 TECTIBRANCHIATA 



onina (Carboniferous), Cylinclrites (Secondary strata), Actaeondla 

 (Cretaceous). 



Fam. 2. Tornatinidae. — Shell spiral, cylindrical, entirely 

 covering the animal ; spire concealed, cephalic disc with two 

 large tentaculiform appendages behind, no radula. Genera : 

 Tornatina ( = Utriculus), Volvula. 



Fam. 3. Sc(vphandridae. — Shell more or less external, covering 

 all or nearly all the animal, spire concealed, cephalic disc simple 

 or notched behind, epipodia well developed, radula with first 

 lateral very large, stomach sometimes with powerful gizzard. 

 Genera: Scapliander (Fig. 287 B) ; Sabatia (Vliocene), Smaragdi- 

 nella, Atys (Fig. 286 D), Cylichna (Fig. 286 C), Amphisphyra. 



Fam. 4. Bullidae. — Shell external or partly internal, spire 

 quite or nearly hidden, cephalic disc broad, without appendages, 

 epipodia often large ; radulausually multiseriate. Genera : Bulla 

 (subg. Haminea), Accra, mantle with long filiform appendage, 

 epipodia touching over the shell ; Cylindrohulla, Volvatella. 



Fam. 5. Aplustridae. — -Shell partly internal, overlaid by the 

 posterior part of the cephalic disc, spire not prominent, epipodia 

 reflected, tentacles auriform. Single genus, Aplustrum (Fig. 286 

 B ; subg. Sydatina). 



Fam. 6. Ringiculidae. — Shell small, solid, covering all the 

 animal ; spire somewhat prominent, aperture narrow, plicated ; 

 peristome thick, sometimes channelled, cephalic disc with a kind 

 of posterior siphon. Genera : Ringicula ; Avellana (Cretaceous). 



Fam. 7. Gastr^opteridac. — Shell completely internal, nautiloid, 

 small ; epipodia very large, rounded, united behind ; cephalic disc 

 simple. Single genus, Gastropteron. 



Fam. 8. Philinidac. — Shell completely internal, thin, slightly 

 spiral ; epipodia thick, cephalic disc large, thick, simple ; stomach 

 usually with powerful gizzard. Genera: Philinc (Fig. 287 E), 

 Colpodaspis, Coloboccphalus, Chclinodura, Phancrophthalmus, Crypt- 

 ophthalmus. 



Fam. 9. Doridiidae. — Shell completely internal, a mere 

 pellicle with a small spiral nucleus, mantle with two posterior 

 lobes and a caudal filament, epipodia reflected. Single genus, 

 Doridium. 



Section II. Aplysioidea. — Shell small, usually not spiral, 

 sometimes absent, no cephalic disc, head prominent, with two 

 pairs of tentacles, epipodia large, more or less reflected. 



