CONCHOLOGY. 
equal sided, open at one or both ends: hinge 
without teeth. 
‘Includes the Mytilus rugosus, and M. Pholadis. 
15. Gastrochena. Sheil transverse, oval, with a 
vast opening in front. Hinge with a_ single 
obscure transverse, somewhat laminar tooth in 
each valve : lateral teeth none. 
Includes Mya dubia. 
16. Savicava, Shell transverse, equivalve, in- 
equilateral, open at one or both ends. Hinge 
without teeth. 
Includes Mytilus rugosus and Mytilus pholadis. 
17. EMatella, Shell transverse, inequivalve, in- 
equilateral, open at the anterior end. Hinge 
with a single tooth in one valve closing between 
two obscure ones in the other: lateral teeth none. 
Includes Solen minutus. 
18, Petricola. Shell transverse, equivalve, in- 
equilateral, open at the anterior end. Hinge with 
two teeth in one valve closing between three in 
the other : lateral teeth none. 
Includes Donax irus, 
19. Vekerirupis. Shell transverse, equivalve, in- 
equilateral, open at the anterior end. Hinge with 
three elongated teeth in each valve, all parallel 
and close together, one of them smaller; lateral 
teeth none. 
Includes Venus perforans, 
20. Anatina, Shell transverse or somewhat orbi- 
eular, inequivalve, open at the anterior or both 
ends. Hinge with a dilated concave tooth pro- 
