CONCHIFEKA. 



301 



Oedee III. 



MOXOMYARIA. 



The animals have only one adductor muscle ; the valves 

 therefore have each only one muscular impression. 



Family 1. — TRIDA CNA CEA. 



The animal has a mantle which, as far as the three 

 openings, is closed completely ; the two lower and hinder 

 openings serve for the egress of the water that has passed 

 the gills, as well as for the anal duct ; the third opening 

 lies above close to the back of the bosses of the shell : the 

 gills are long and narrow, the upper one much narrower than 

 the under or inner one, and connected therewith almost 

 its entire length; the mouth is oval, with two large 

 narrow lips, at the end of which, on each side, are a pair 

 of narrow, pointed labial tentacles. The shell is regular, 

 equivalve ; the hinge has under the boss two oblique, 

 unequal teeth ; the ligament is external at the edge ; one 

 muscular impression, two adductor muscles exist, but they 

 are so very approximate that they appear but one. Found 

 living in the Indian, Chinese, and South seas, growing to 

 an enormous size. — Xot known as fossils. 



Teidacna. Brug. (Pelvis Mergele v. Muhlf ; Hip- 

 popus Gray.) — The shell 

 and animal are described 

 in the family ; the foot of 

 the latter is thick, cylin- 

 drical, and bearing a bys- 

 sus ; the part of the mantle 



, . , 1 >1 n Tridacna gigas 



which surrounds the toot 



