coifcsrPEitA. 471 



In Derbysliire tlie miissel-band is wrougM, like marble, into 



Tases. 



? Mtoconcha, J. Sowerby. 



Type^ M. crassa, PL XIX. , Eig. 25, {My a, mussel, concha, 

 sbell.) 



Shell oblong, thick, with nearly terminal depressed nmbones ; 

 ligament external, supported by long, narrow, appressed plates ; 

 hinge thick, with an oblique tooth in the right yalve ; 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 Mytilidce 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 a,ged examples 

 of Cardita orbicularis and Gypricardia vellicata. 



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



Sub-genus. ? Hippopodium (ponderosum, Sowerby), Coneybeare. 

 Lias, Europe. Shell oblong, thick, yentricose ; umbones large ; 

 ligament external ; ventral margin sinuated ; hinge with one 

 thick, oblique tooth in each valve, sometimes 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. 



Caedita, Bruguiere. 



Synonyms, Mytilicardia and Cardiocardita (ajar), Bl. Arcinella, 

 Oken. 



Type, C. calyculata, PL XX., Eig. 5. 



Etymology, cardia, the heart. 



Shell oblong, 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, tapering behind, and 

 united together, the outer pair narrowest. 



C. pectu7iculus, BruguieSre, {Mytilicardia, Blainville), has an 

 anterior tooth. 0. concamerata, Bruguiere, found at the Cape, 

 has a remarkable cup-like inflection of the ventral margin ot 

 eadi valve. 



