430 TECTIBRANCHIATA chap. 



Actaeonina (Carboniferous), Cylindrites (Secondary strata), 

 Actaeonella (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 (^=Utrieulus^^ Volvula. 



Fam. 3. Scajyhandridae. — Shell more or less external, cover- 

 ing 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: Scaphander (Fig. 287 B); Sahatia (Pliocene), Smaragdi- 

 nella^ Atys (Fig. 286 D), Cylichna (Fig. 286 C), Amj^hisphyra. 



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

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

 epipodia often large ; radula usually multiseriate. Genera : Bidla 

 (subg. Haminea)^ Acera^ 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. Hydatina). 



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 : Ringicida ; Avellana (Cretaceous). 



Fam. 7. G-astropteridae. — Shell completely internal, nauti- 

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

 disc simple. Single genus, Gastropteron. 



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

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

 usually with powerful gizzard. Genera : Philine (Fig. 287 

 E), Colpodaspis^ Oolobocejjhalus, Chelinodura, PhaneropJithalmus, 

 Cryptophthahnus. 



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. 



