Fig. 310.—Teredo navalis L.: V, valves of shell; T, tube; P, pallets; SS, siphons. (After Möbius.)
Fam. 2. Teredinidae.—Animal vermiform, ctenidia mainly within the branchial siphon, siphons very long, with two calcareous appendages (“pallets”) near the anterior end, shell very small, continued into a long calcareous tube, valves deeply notched, internal apophysis as in Pholadidae. Lias——. Single genus, Teredo (Fig. [310]).
Sub-order VII. Anatinacea.—External branchial fold directed dorsally, not reflected, sexes united, ovaries and testes with separate orifices, mantle edges largely united, byssus usually absent, two adductor muscles, pallial line variable, shell usually nacreous within.
Fam. 1. Pandoridae.—Siphons short, largely united, foot tongue-shaped; shell free or fixed, inequivalve, semi-lunar, or subtriangular, ligament often with calcareous ossicle, pallial line complete or with slight sinus. Cretaceous——. Genera: Pandora, Myodora, Myochama.
Fam. 2. Chamostreidae.—Shell fixed, Chama-like, thick, umbones spiral, ligament with ossicle. Single genus, Chamostrea.
Fam. 3. Verticordiidae.—Siphons not prolonged; shell heart-shaped, umbones prominent, spiral, ligament with an ossicle, pallial line complete. Miocene——. Genera: Verticordia, Mytilimeria, Lyonsiella.
Fam. 4. Lyonsiidae.—Foot short, byssiferous, siphons short, separate, shell inequivalve, hinge-teeth usually absent, ligament and ossicle in an internal groove. Eocene——. Single genus, Lyonsia.
Fig. 311.—Myochama Stutchburyi A. Ad., attached to Circe undatina Lam., Moreton Bay.