MOLLUSCS, VERMES AND HYDROZOA 



the hinge, which has the margin compressed and considerably curved. 

 The surface is smooth, except at the posterior portion, where it is wrinkled 

 and shows a number of radiations from the upper edge of the umbone. 



FIG. i88. Anadonta cataracla. Adult. 



The color is a deep clear green, indistinctly radiated with a darker green 

 and brown. On the inside the silvery nacre is tinged with blue and yellow 

 and has a greenish margin. It reaches a large size and may be 4^ inches 

 long, 2^ inches broad and i^ inch thick, though most of these mussels 

 are about 3 inches long. It usually inhabits ponds and still water and 

 occurs quite generally on the Eastern Atlantic slope. 



A. implicata. Fig. 189, is a characteristic species with transversely 

 oblong, sub-oval, thick, opaque, strong and heavy valves, almost as thick 

 as broad; having the umbones distinct and usually eroded. It has ridges 

 from the lower posterior edge of 

 the umbone to the angular tip 

 of the posterior edge. The 

 valves are broadest behind the 

 middle; the hinge margin is 

 slightly curved. The outer sur- 

 face is rough with coarse lines of 

 growth, of a yellowish-olive color 

 somewhat darker above, and the "^- '^9- ■^""""•ta impucat^. Young shell. 



lines are marked with a dull brown. Older shells have a delicate salmon 

 or flesh-color and the younger a silvery tint on the inside. It grows to 4 

 inches long, 2^^ inches broad and i J^ inches thick, but average shells 

 are usually about 3 inches long or under. It inhabits ponds and still 

 water throughout the Eastern and Middle States but has a quite general 

 distribution. This mussel is more elongate, narrower and thicker than 

 the foregoing and may be distinguished by its obtuse ridge. The margin 

 is also more convex. 



244 



