458 EULAMELLIBRANCHIATA — ANATINACEA chap. 



within the branchial siphon, siphons very long, with two calca- 

 reous 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, semilunar, or 

 sub triangular, ligament often with calcareous ossicle, pallial line 



complete or with slight sinus. 

 Cretaceous . Genera; Pan- 

 dora, Myodora^ Myochama. 



Fam. 2. Chamostreidae. — Shell 

 fixed, Chama-like, thick, umbones 

 spiral, ligament with ossicle. 

 Single genus, Ohamostrea. 



Fam. 3. Verticordiidae. — 

 Siphons not prolonged ; shell heart- 

 shaped, umbones prominent, spiral, 

 ligament with an ossicle, pallial 



Fig. zn. — Mijochama stutchhuryi line complete. Miocene . Gen- 



A. Ad., attached to Circe unda- gp^ . Yevticordia. Mytilimeria. Ly- 



Una Lam., Moreton Bay. '^ 



onsiella. 



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. 



Fam. 5. Ceromyidae. — Shell inequivalve, large, heart or wedge 

 shaped, hinge toothless, ligament internal in one valve, external 

 in the other. Secondary strata . Genera : Ceromya, G-resslya. 



Fam. 6. Arcomyidae. — Shell equivalve, thin, surface finely 

 granulated, hinge toothless, cardinal edge dentiform, ligament 



external. Secondary and Tertiary strata . Genera : Arco- 



mya, Goniomya, Pleuromya^ Machomya. 



Fam. 7. Anatmidae. — A fourth (?byssal) pallial orifice, 

 siphons long, separate or fused; shell thin, sometimes inequivalve, 



