Section I. Bulloidea.--Shell More or Less Spiral, Internal or External,

epipodia more or less developed, a broad cephalic disc, distinct from the dorsal region, usually no tentacles, eyes sessile.

FAM. 1. Actaeonidae.--Shell spiral, solid, entirely covering the animal; spire generally prominent, operculum corneous, visceral loop streptoneurous, no epipodia, radula multiseriate, teeth numerous, very small. Carboniferous ----. Genera: Actaeon (Fig. 286a); Volvaria (Tertiary), Fortisia (Eocene) 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 (= Utriculus), Volvula.

FAM. 3. Scaphandridae.--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: Scaphander (Fig. 287 B); Sabatia (Pliocene), Smaragdinella, 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; radula usually multiseriate. Genera: Bulla (subg. Haminea), Acera, mantle with long filiform appendage, epipodia touching over the shell; Cylindrobulla, 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: Ringicula; Avellana (Cretaceous).

FAM. 7. Gastropteridae.--Shell completely internal, nautiloid, 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, Colobocephalus, Chelinodura, Phanerophthalmus, Cryptophthalmus.

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.