CLA8S I 



PELECYPODA 



491 



minent prosogyrous heaJcs ; adductor scars sub-equal ; pedal scar adjacent ; area not dis- 

 tinctly limited ; ligament and resilium external, parivincular, set in a deep groove, con- 

 tiniious to the heaks ; complete armature of the hinge with an inconstant posterior lateral 

 in each valve, and rarely, an anterior lateral dose to the cardinals ; cardinal formula 



pqYqT) ihe teeth lamelliform, and very variable in details of form. Jura to Receiit, 



Many species have been referred to this group solely on account of their having gyrate 

 beaks. Tlie Paleozoic and many Mesozoic species so referred must be separated from 

 Isocardia. 



Isocardia Lam. (Figs. 805, 806). Inflated, smootli or concentrically striated ; 

 beaks distant, iniich produced, prosogyrate. Jura to Receiit 



B 



B'k;. 8UÖ. 

 Isocardia striata d'Orb. Portlandian ; Cirey, Haute-Marne (after Loriol). 



Meiocardia Adams. Keeled, concentrically ribbed. Tertiary and Recent. 

 ? Glisocolus Gabb. Cretaceous ; North America. 



Fio. 806. 

 Hinge of Isocardia lunulata Nyst. Crag ; Antwerp. 



Family 30. Vesicomyacidae Dali. 



Shell as in the Isocardiidae, hut with low and inconspicuous heaks, the valves more 

 elongated, and the lunule delimited hy a sharp groove; cardinal formula piqiq^q ' 

 Tertiary and Recent. 



Callogonia Dali. Pallial line deeply sinuated, and a distinct anterior lateral close 

 to tlie cardinal teetli, Recent ; abyssal. 



Vesicomya Dali. {Gallocardia auct., non Adams). Rounded or Tapetiform, com- 

 pressed, or not infiated, witli low, inconspicuous, non -gyrate beaks. Eocene and Recent. 



D. Teleodonta. 



The most perfected type of modern teeth, to which, in addition to the typical (10101) 

 cardinal series of the ordinary Teleodesmacea, there is added in the most specialised types 

 (Veneridae, Mactridae) either a roughened area (Veiius), a series of extra cardinals 

 (Tivela), or accessory lamellae (Mactra), rendering the hinge rnorr < ifinent, or covvphcdfrd. 



