20 THE ELEMENTS 



some are single and large, others 

 numerous and small, orbicular, spatuli- 

 form, laminated, &c. Some hinges 

 have no visible teeth, and are termed 

 inarticulate;* those with few teeth 

 are termed articulate;^ and those 

 with many teeth multiarticulate.% 

 Plate 1st, figures 6th and 8th, g g g g. 



Primary Teeth, are those teeth in 

 general about the centre of the hinge, 

 and are for the most part broad, large, 

 and distinct, and often elevated ; and 

 in general are inserted in a cavity in 

 the opposite valve. They however 

 differ very much in some shells, but 

 may easily be distinguished. Plate 

 4th, figures 1st, 3d and 7th, aaaaa. 



Lateral Teeth$ are teeth which di- 

 verge from the umbo, and are in gene- 

 ral long and flat, often double, and 

 divided by a groove or hollow. Plate 



* When a primary tooth has a groove or hollow in its cen- 

 tre, it is called complicated. Plate 4th, fig. 6th, e. 



t Plate 4th, figures 1st and 1 2th. t Plate 4th, figures 2nd, 

 3d, 4th, &c. § Plate 4th, fig. 10th. 



