CLASS I 



PELECYPODA 



485 



Family 17. Lucinidae Fleming. 



Shell substance porcellanous or chalky, usually ivitli inconspicuous or dehiscent 

 epidermis, rounded, variably sculptured ; valves equal, free, closed, with low, prosocoelous 



Fig. 790. 

 Luuina ( Milthd) gigantea Desli. Eocene (Calcaire Grossier) ; Grigiion, near Paris. 2/3. 



beaks ; adductor and pedal scars adjacent or distinct, the latter small ; anterior adductor 

 elongated, largely within the pallial line, which is not sinuate ; area tvithin the pallial 

 line often granular or iiimctate ; cardinal area small, often deeply impressed; ligament 

 and resilium sub-internal, set in a deep groove, but usually more or less visible externally ; 

 hinge-plate distinct ; lateral laminae distant from the cardinals, anterior and posterior 

 in the right, vnth corresponding sockets in the left valve ; cardinal teeth radial, formula 



=^^ — , the posterior tooth larger and often bifid, but any or all of the teeth may be obsolete 



or absent. Silurian to Eeceut. 



Paracyclas Hall. Rounded, tliin-slielled, concentrically striated ; no lunule ; hinge 

 unlvno^\^l. Devonian. 



Lucina Brug. (Figs. 790-793). Rounded, convex or lenticular, usually with a 



Fio. 791. 



Liwina {My rim) columbclla Lam. Miocene ; 

 Steinabrunn, near Vienna. 



Fig. 792. 



Lucina {Prolucina) prisca His. Silurian ; Gotland. 

 Internal mould (after Roemer). 



lunule ; with delicate, concentric, or more rarely radial sculpture ; dentition usually 

 normal, the laterals developed. Represented Ijy upwards of 300 fossil and 100 recent 

 species. (?) Silurian, Trias to Recent. 



