MOLLUSCS, VERMES AND HYDROZOA 



Margaritana. This genus of the Unionidae 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. 1 90, 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. 



Adult. 



190. Margaritana margaritifera, 



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. The 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 in the right. The mussel is 4 J^ inches long, 2 inches broad 

 and 1 ^ 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- 

 ing darker green or brownish lines. 



FIG. 191. Margaritana marginata. Nearly adult. 



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