
MOLLUSCS, VERMES AND HYDROZOA 

Marcarirana. This genus of the Unionide may be found in most 
running streams of fresh water, and has the valves transversely elongated, 
inequilateral, and the hinge differs from the Unios, with which some of 
the species have been classed by Conchologists. 
M. margaritifera, Fig. 190, has the ovate or kidney-shaped thick and 
strong valves transversely much elongated, with the umbones but slightly 
raised above the line of the hinge and usually much eroded; and the hinge 

FIG. 190. Margaritana margaritifera. Adult. 
and basal margin nearly as broad before as behind the hinge, wnich is 
usually curved and nearly parallel, with the tips slightly truncated. The 
surface is waved with lines of growth and loosely wrinkled posteriorly and 
towards the margin. ‘he outside is pitchy-black, the inside has a green- 
ish border at the margin while the nacre is bluish-white shading to flesh- 
color in the centre of the valves. There are two cardinal teeth in the left 
valve and one inthe right. The mussel is 41% inches long, 2 inches broad 
and 114 inches thick, probably the largest freshwater mussel of the Atlantic 
slope, very generally distributed in the Eastern and Middle States. 
M. marginata, Fig. 191, has thin-ovate, anteriorly wedge-shaped 
valves with small but elevated umbones, usually somewhat eroded. The 
posterior hinge margin declines abruptly to form a rounded tip and a well- 
defined ridge extends from the um- 
bone to the lower forward edge and 
the valves show rounded wrinkles and 
well-defined lines of growth. The 
color is a polished olive-green mot- 
tled with lighter and darker shades 
and having broken or obscure radiat- 

FIG. 191. Margaritana marginata. Nearly adult, ing darker green or brownish lines. 
24.5 
