viii A SYNOPSIS OF 



4. MYA.— Plate 2. 



Animal, an Ascidia. 



Shell, bivalve, generally gaping at one end. Hinge, for the most 

 part, with a single solid, thick, broad tooth, strongly attached 

 by cartilage, but not inserted into the opposite valve. 



5. SOLEN.— Plate 3. 

 Animal, an Ascidia. 

 Shell, bivalve, equivalve, elongated transversely ; open at both ends. 



Hinge with an awl-shaped reflex tooth, often double ; not 



serted into the opposite valve. 



in- 



6. TELLINA.— Plate 3. 



Animal, a Tethys. 



Shelly bivalve, generally flattish, sometimes orbicular, anterior end 

 often produced into an angular beak. Hinge usually with three 

 teeth ; lateral teeth in one of the valves flat; often remote. 



7. CARDIUM.— Plate 5. 

 Animal^ a Tethys. 



Shtll, bivalve, equivalve, nearly equilateral, somewhat heart-shaped, 



ribbed longitudinally ; beaks prominent, valves toothed or 



plaited on their internal margin. Hinge with four teeth in each 



valve; the two cardinal teeth near together, and alternating 



with the opposite ; the two lateral teeth remote and inserted. 



8. MACTRA— Plate 6. 

 Animal, a Tethys. 



Shellj bivalve, valves unequal at the sides ; subtriangular ; beaks 

 prominent. Hinge with the middle tooth spoon-shaped, having 

 a small cavity on each side ; lateral teeth remote, locking into 

 the opposite valves. 



