Diagnosis: Small, subtriangular to subpentagonal in outline, smooth but sometimes with obscure marginal plicae; uniplication generally flat-topped, sometimes rounded; anterior commissure with or without variable dentition (secondary plication); beak small, straight to sub-erect; beak ridges sub-mesothyridid; foramen small, with well-developed collar extending below deltidial plates; deltidial plates conjunct as a symphytium; hinge teeth small, dental plates (lamellae) present but obscured in older individuals of some species due to swelling of hinge tooth base. Median septum reduced to a ridge or low keel; cardinal process absent or only weakly developed; outer and inner socket ridges well-developed, socket interiors with distinct corrugations or ridges; outer hinge plates small and narrow-triangular; crura falciform, distal ends broad and truncated, truncated edge with or without fine serration; crural bases variably thickened, increasingly swollen to medially coalescent in older individuals, overgrowing the outer hinge plates laterally; Inner hinge plates absent. Lophophore spirolophous.

Diagnosis modified from volume 4 of the Treatise on Invertebrate Paleontology (2002), and original diagnosis[1]

Etymology: Genus name alludes to a smaller form alike the sister genus Basiliola (-ella suffix indicating a diminutive form).

[1] Originally diagnosis (d’Hondt, 1987; p. 39): “Basiliolidae à suture multiplissée du côté antérieur, à coquille lisse de forme triangulaire, à septum médian réduit à une carène très peu saillante. Crura renforcées à leur base. Crochet saillant submésothyride.” = Basiliolidae with multi-fold commissure on anterior side, with smooth triangular-shaped shell, with a median septum reduced to a very slightly projecting ridge. Crura reinforced at their base. Beak projecting, sub-mesothyridid.