CONCHIFERA. 301 



Shell oblong, with an oblique posterior ridge; umbones anterior de- 

 pressed; ligament external, in deep and narrow grooves ; cardinal teeth 2:2, 

 laterals 1 — 1 in each valve, sometimes obscui-e ; muscular impressions oval, 

 (of two elements) ; pallial line simple. 



Animal (of C. solenoides) with mantle-lobes united, cii-rated behind; 

 pedal opening moderate ; foot small, compressed, with a large byssal pore 

 near the heel ; siphons short, conical, unequal, cirrated externally ; orifices 

 fringed ; palpi small ; gills unequal, the outer narrower and shorter, deeply 

 lamellated, united posteriorly, the inner prolonged between the palpi. 



Distr. 13 sp. Red Sea, India, Australia. In crevices of rock and coral. 



Fossil, 60 sp. L. Silurian — . N. America, Europe. 



? Sub-genera. Coralliophaga, Bl. C. coraUiophaga, Lam, Shell long, 

 cylindrical, thin, slightly gaping behind; hinge-teeth 2:2, and a laminar 

 posterior tooth ; pallial line with a wide and shallow sinus, Distr. 2 sp. 

 Medit, in the burrows of the Lithodoymis ; sometimes two or three dead 

 shells are found one within the other, besides the original owner of the ceU. 

 ? Cgpricardites, Conrad (part). An. Geol. Rep. 1841. (Sanguinolites, 

 M'Coy), Employed for Cypricardia-shaped shells of the palaeozoic rocks; 

 some of them are more nearly related to Modiola (v. Modiolopsis, p. 266) 

 but they bear no resemblance to Sanguinolaria. 



Pleurophorus, King, 1848. 



Type, P. costatus, Brown. Permian, England, (Pal. Trans, 1850, 

 PI. XV, fig, 13—20.) 



Sgn. ? Cleidophorus, Hall (cast only). Unionites, Wissm. ? Mseonia, Dana. 



Shell oblong ; dorsal area defined by a line, or keel ; umbones anterior, 

 depressed; hinge-teeth 2.2 ; laterals 1.1 ; elongated posterior; anterior ad- 

 ductor impression deep, with a small pedal scar close to it, and bounded pos- 

 teriorly by a strong rib from the hinge ; pallial line simple 



Fossil, L. Silurian — Trias. U. States; Europe, N. S.Wales, Tasmania. 



? Cardilia, Deshayes. 



I'gpe, C. semisulcata, PL XVIII. fig. 18, Syn. Hemicyclonosta, Desh. 



Shell oblong, ventricose, cordate ; beaks prominent, sub-spiral ; hinge with 

 a small tooth and dental pit in each valve ; ligament partly internal con- 

 tained 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. 



Distr. 2 sp. Chinese Sea; Moluccas. 



Fossil, 2 sp. Eocene — . France, Piedmont. 



Megalodon, J. Sowerby. 

 Type, M. cucullatus, PI. XIX. fig, 19. {Megas, large, odous, tooth,) 

 Shell oblong, smooth or keeled ; ligament external ; huige-teeth 1:2, thick ; 



