Subfamily Pachylasmatinae Utinomi, 1968

Remarks. The Pachylasmatinae, as per the landmark revision of Jones (2000), encompasses five genera; Eutomolasma Jones, 2000: 166 (four species), Microlasma Jones, 2000: 177 (four species), Pachylasma Darwin, 1854: 185 (eight species), Eurylasma Jones, 2000: 201 (three species), and Tetrapachylasma Foster, 1988: 215 (five species). All, except the type of Tetrapachylasma, have an eight-plated stage early in ontogeny, albeit the rostrum is generally tripartite, RL-R-RL, and the carinolaterals, CL1-CL2, are partially concrescent. These tendencies are preludes to the pure four-platedness seen in Tetrapachylasma s.s. Therefore, acceptance of Tetrapachylasma as a monophyletic taxon must be viewed with caution. The wall of the new genus, to be proposed below, is like that of a Tetrapachylasma s.s. in that it displays not a hint of having had more than four plates making up its wall early in ontogeny. On the other hand, as we shall see, it displays the most generalized opercular plates known to any balanomorph and, therefore, stands well apart from other pachylasmatines including the other species of Tetrapachylasma .