S-type ventral organization
A term so named because of the sigmoidal nature of the sulcus. The sixth precingular plate (1i) tends to have a triangular shape, with anteriorly converging lateral margins and a narrow, typically planate anterior margin. The fourth apical plate or its homologue (A) tends to be (but is not always) long and predominantly ventral, and contacts the anterior sulcal plate (ai). See also L-type ventral organization. Refer to Text-Figure 82.