Definition from Wiktionary, the free dictionary
- (archaic) A non-taxonomic, informal classification, within phylum Mollusca - those in the classes having heads: Cephalopoda, Pteropoda and Gasteropoda
1854, Philip Henry Gosse, Natural History, page 57:
- Naturalists arrange the Mollusca in six classes, named Cephalopoda, Pteropoda, Gasteropoda, Conchifera, Brachiopoda, and Tunicata. Of these the first three are sometimes distinguished as Encephala, or furnished with a head; the last three as Acephala, being destitute of that organ.