Sigalion, [313]

Silliman, on Nemertinea, [101], [109], [118]

Silurian, Polychaeta, [301]

Sinus, in Polyzoa, [482], [484], [525]

Siphon, of Capitelliformia, [272], [305];

of Gephyrea, [436]

Siphonogaster, [353], [368]

Siphonostoma, [334];

commensal, [298]

Sipunculoidea, [412], [420], [446];