118 



Figure. 



Cyclas counea. PI. 37. Fig. 199. Shell, showing its small cardinal 

 and rather remote lateral teeth. 



Family 7. NYMPHACEA. 



Shell; either transverse or orbicular, sometimes gaping at the 



sides, posterior side always rounded, anterior mostly attenuated 



hy a depression radiating from the umboes, which is sometimes 



Jlexuous ; hinge composed mostly of small central cardinal teeth, 



with sometimes a callosity on the margin. 



The Lamarckian family of Nymjohacea is not well constituted. The Do- 

 nax and Tellen have long widely separated siphons, while the Lucina 

 and Corbis have none, the siphonal orifices being sessile ; and Galeomma 

 differs more than all in having the mantle closed, like Tridacna, with only 



