ANATINAD^. 



53 



Gastrochcena (Spengler). Shell -wedge-shaped, 

 widely gaping; hinge toothless. Animal — siphons 

 separate only at the tips; orifices simply fringed; 

 the whole enclosed in a flask-like calcareous tube. 



G. modiolina. Fig. 64 ; n. s. 



Saxicava (De Bellevue). Shell oblong ; hinge 

 with cardinal teeth. No tube. 



S. arctica. 



rugosa. Fig. 65 ; n. s. 



66 



65 



67 



Family III. Anatinad^. 



Shell usually unequal-sided, thin, granular on the 

 outside, pearly within ; ligament external, thin; car- 

 tilage internal, placed in corresponding pits,andoften 

 furnished with a free shelly piece [ossicle) ; muscu- 

 lar impressions faint, the front one lengthened ; 

 pallial line usually sinuated. Animal with a closed 

 mantle; siphons usually long, more or less united, 

 fringed; gills single on each side; foot small, 

 tone'ue-shaped. 



Pandora (Lamk.). Shell pearly, the left valve 

 convex, the other flat ; hinge teeth J with pits. 



