330 



POPULAR CONCHOLOGY. 



the hole in the dorsal or upper valve is more under than 

 in the summit of the boss, and is oval or triangular; the 

 deltidium is formed of two, generally separate pieces ; the 

 hinge has two distinct teeth in the upper valve fitting into 

 two sockets in that opposite. The inner scaffold consists 

 of a central plate which springs from the under valve, and 

 two loop-shaped branches which project from the hinge, 

 and are supported by this middle plate ; the shell has 

 dichotomous ribs, and for the most part in the upper 

 valve a sinus or indentation, to which a saddle-shaped pro- 

 tuberance in the under valve answers. — 2 species ; also 

 fossil. 



The living species are T. truncata^ and chilensis from 

 the Mediterranean. 



Magas. Sow. — Shell equilateral, inequivalve, one 

 valve convex, with a triangular area, 

 divided by an angular sinus in the centre ; 

 the other valve flat, with a straight hinge 

 line, and two small projections; a partial 

 longitudinal septum with appendages at- 

 tached to the hinge within ; differing from 

 Terebratula in having a triangular disk, 

 and not a circular perforation.* — Fossil. 



One species found near Norwich. Mr. Magas pumiius. 

 Sowerby observes that this singular fossil 

 shell (M. pumiius) " when magnified is found to be curiously 

 punctured in a minute quincunx order, which appears to 

 depend on the construction of it, as in most of the tribe 

 related to the Terebratula ; it is generally most apparent 

 within the substance." 



Bouciiardia. Davidson. — Shell inequivalve, oval, 



* Sowerby's Mineral Conch. 



