CONCHIFERA. 469 
? Sub-genus. Redonia, Rouault, Bull Soc. Geol., 8, 362. Shell 
oval, tumid; hinge with cardinal and posterior teeth ; anterior 
adductor bounded byaridge. fossil, Lower Silurian, Brittany, 
Portugal. (Sharpe.) 
Fossil, 5 species. Lower Silurian—Trias. United States, 
Europe, New South Wales, Tasmania. 4 
? CARDILIA, Deshayes. 
Type, OC. semisulcata, Pl. XVIII., Fig. 18. 
Synonym, Hemicyclonosta, Deshayes. 
Shell oblong, ventricose, cordate; beaks prominent, sub- 
spiral; hinge with a small tooth and dental pit in each valve; 
ligament partly internal contained in a spoon-shaped inflection ; 
anterior muscular scar long, with a pedal scar above; posterior 
adductor impression on a prominent sub-spiral plate; pallial 
line simple. 
Distribution, 2 species. Chinese Sea, Moluccas. 
Fossil, 2 species. Hocene—. France, Piedmont. 
MEGALODON, J. Sowerby. 
Type, M. cucullatus, Pl. XIX., Fig. 19. (Megas, large, odous, 
tooth.) 
Shell oblong, smooth or keeled; ligament external; hinge- 
teeth 1.2, thick; laterals 1.1, posterior; anterior adductor 
impression deep, with a raised margin, and a small pedal scar 
behind it. . 
In the typical species the beaks are sub-spiral, the lateral] 
teeth obscure, and the posterior adductors bounded by prominent 
ridges. 
Fossil, 14 species. Upper Silurian—Devyonian. United States, 
Europe. 
Sub-genera. ? Goldfussia (nautiloides), Castlenau. Umbones 
spiral; anterior side concentrically furrowed; posterior side 
with two oblique ridges. Jfossil, Silurian, United States. 
Megaloma (Canadensis), Hall, 1852. Upper Silurian, Canada. 
Umbones very thick, hinge-teeth rugged, almost obliterated 
with age; posterior lateral teeth 1.1; no muscular ridges. 
PAcHYDOMUS (Morris), J. Sowerby. 
Etymology, pachus, thick, domos, house. 
Synonyms, Astartila, Dana. ? Cleobis (grandis), Dana. 
? Pyramus (ellipticus), D. =Notomya, M‘Coy. 
