722 



LAMELLIBRANCHIATA. 



very inequilateral, posteriorly attenuated, and not ventricose. The 

 ligament is external, in a deep furrow, and the cardinal teeth are 

 feebly developed or wanting, while there is a single prominent 

 lateral tooth on each side. The surface is smooth or concentrically 

 striated, and the beaks are not eroded. The genus is extinct, and 

 is confined to the Triassic and Jurassic rocks. Trigonodus, of the 

 Trias (fig. 597, c), is closely allied to Cardinia, but the cardinal 



Fig. 597.— Types of Ca7-diniidce. A, Anthracosia Lottneri, from the Coal-measures of Ger- 

 many; b, Interior of the right valve of Cardinia Listeri, Jurassic; c, Cast of the interior and 

 hinge-line of Trigonodus Sandbergi, from the Trias of Wurtemberg ; d, Interior of the left valve 

 of Guerangeria Davousti, from the Inferior Devonian of France. (After Zittel, CEhlert, and 

 Woodward.) 



teeth are more fully developed, the right valve having one and the 

 left valve two. Various Palaeozoic shells have been referred to 

 Cardinia, but the true affinities of these are doubtful. 



We may place in this family the Devonian and Carboniferous 

 genus Carbonicola, comprising Unionoid Bivalves, with thick shells, 

 an external ligament, and a concentrically-striated surface. The 

 beaks are not eroded • and the hinge has a thick cardinal tooth in 

 the right valve, with a long lamellar lateral tooth on each side. 



The genus Anthracosia comprises a number of thin-shelled 

 Bivalves in which the shell is long-oval and inequilateral (fig. 

 597, a), and the surface is smooth or concentrically-striated. The 

 ligament is external, and the hinge seems to have been provided 

 with a single cardinal tooth in each valve, without lateral teeth. 

 The Anthracosia are found in abundance in parts of the Coal- 

 measures and Lower Permian series, and they may perhaps have 

 been inhabitants of brackish water. 



Lastly, we may place here the Lower Devonian genus Gueran- 



