CONCHIFERA. 303 



scure, laterals 1 0, 1, remote, prominent ; adductor impressions deep 

 pallial line simple. 



Fossil, 20 sp. Lias . Inf. Oolite, Europe ; along with marine shells. 



Sub-genus? Anthracosia, King, 1844; Unio sub-constrictus. Sby. 

 U. Sil. Carb. 40 sp. They occur in the valuable layers of clay-ironstone 

 called " mussel-bands," associated with Nautili, Discina, &c. In Derbyshire 

 the mussel-band is wrought, like marble, into vases. 



? MTOCONCHA, J. Sowerby. 



Type, M. crassa, PI. XIX. tig. 25. (Mya, mussel, concha, shell.) 



Shell oblong, thick, with nearly terminal depressed umbones ; ligament 

 external, supported by long narrow appressed plates ; hinge thick, with an 

 oblique tooth in the right valve ; anterior muscular impression round and 

 deep, with a small pedal scar behind it ; posterior impression large, single ; 

 pallial line simple. 



This shell, which is not nacreous inside, is distinguished from any of the 

 'Mytilida by the form of its ligamental plates and muscular impressions ; the 

 hinge-tooth is usually overgrown and nearly obliterated by the hinge-margin 

 as in aged examples of Cardita orbicularis and Cypricardia vellicata. 



Fossil, 26 sp. Permian Miocene. (D'Orb.) Europe. 



Sub -genus. ? Hippopodium (ponderosum, Sby.) Coneybeare. Lias, Europe. 

 Shell oblong, thick, ventricose ; umbones large ; ligament external ; ventral 

 margin sinuated; hinge with one thick, oblique tooth in each valve, some- 

 times nearly obsolete; pallial line simple; anterior muscular scar deep. 

 This shell appears to be a ponderous form of Cypricardia or Cardita ; it is a 

 characteristic fossil of the English Lias, but only very aged examples have 

 been found. 



CARDITA, Bruguiere. 



St/n. Mytilicardia and Cardiocardita, (ajar) Bl. Arcinella, Oken. 



Type, C. calyculata, PI. XX. fig. 5. Etym. Cardia, the heart. 



Shell objong, radiately ribbed ; ligament external ; margins toothed ; 

 hinge-teeth 1:2, and an elongated posterior tooth; pallial line simple; 

 anterior pedal scar close to adductor. 



Animal with the mantle lobes free, except between the siphonal orifices ; 

 branchial margin with conspicuous cirri ; foot rounded and grooved, spinning 

 a byssus ; labial palpi short, triangular, plaited ; gills rounded in front, taper- 

 ing behind and united together, the outer pair narrowest. 



C. pectunculus, Brug. (Mytilicardia, Bl.) has an anterior tooth. C. con- 

 eamerata, Brug. found at the Cape, has a remarkable cup-like inflection of the 

 ventral margin of each valve. 



Sub-genus. Venericardia, Lam. V, ajar, PL XX. fig. 6. Shell cordate, 

 ventricose ; hinge without lateral teeth. Animal locomotive, with a sickle- 

 shaped foot like the cockles. 



P 



