Agnathous

The Onchidiidæ are described as agnathous, but I am confident of having observed the jaw figured.

The mouth is a transverse slit, which shows no teeth, nor any jaws properly so called, and therefore affords an apparent support to the agnathous theory of the Ostracodermi.

This and related agnathous (jawless), finless forms inhabited shallow seas or estuarine habitats[…].

Parenthetically, this line treatment suggests an attempt to mimic the agnathous (jawless) head, if we suppose that the jaw area was colored suitably dark in contrast to the face proper.

Dr Underhill exhibited an agnathous and hydrocephalic fœtus. This was an instance of the rare abnormality due to defect of the lower jaw.

Upon this view an agnathous fœtus may be regarded as sometimes due to a posterior dichotomy, which has ultimately become a complete separation, and in which the two fœtuses have developed equally during a considerable part of intra-uterine life.

In all the neonates examined from the partially agnathous strain, there was no obvious agenesia of the lower mandible.