﻿UNITED STATES. 227 



quite dark brown and scarcely present any rays. The young are usually bright green 

 and beautifully rayed. Some individuals are more inflated than others. The teeth 

 are sometimes so small that it might be taken for 'an Anodonta, while in others they 

 are larger and more tuberculate, reminding us of the genus Monocondylcea, but the 

 teeth do not close in the same manner. 



Margaritana Etowahensis. PL 31, fig. 110. 



Testa lsevi, elliptica, subconipressa, ad lateris planulatis, inaequilaterali; valvulis tenuibus, antice paulisper 

 crassioribus ; natibus prominulis, ad apices rugoso-undulatis ; epidermide luteola, postice obsolete 

 radiata; dentibus cardinalibus parvissimis, ereetis, tuberculato-cotupressis, in utroque valvulo unicis ; 

 margarita cserulea et iridescente. 



Shell smooth, elliptical, rather compressed, flattened at the sides, inequilateral ; 



valves thin, a little thicker before ; beaks a little prominent, rugosely undulate at the 



tips ; epidermis yellowish and obsoletely radiate behind ; cardinal teeth very small, 



erect, compressed, tuberculate and single in both valves; nacre bluish and iridescent. 



Proc. Acad. Nat. Sci., 1858, p. 138. 



Hah. — Tennessee, Dr. T roost. Etowah River, Georgia, Rev. G. White. 



My cabinet and cabinet of Mr. White. 

 Diam. - 6, Length 11, Breadth 2 inches. 



Shell smooth, elliptical, rather compressed, flattened at the sides, rounded before, 

 inequilateral ; substance of the shell thin, very little thickened before ; beaks some- 

 what prominent, with several rugose undulations at the tips; ligament rather short, 

 somewhat thick and light brown ; epidermis yellowish, obsoletely radiate behind, 

 with distant, well marked, broad marks of growth, which give the exterior a strong 

 banded appearance; umbonial slope slightly raised and rounded; posterior slope 

 carinate ; anterior cicatrices confluent and slightly impressed ; jxisterior cicatrices 

 large and confluent ; dorsal cicatrices placed under the plate above the centre of the 

 cavity of the beaks; cavity of the shell shallow and wide; cavity of the beaks rather 

 shallow and angular; nacre bluish and iridescent. 



RemarJcs. — A single half grown, poor specimen of this species was received from 

 Dr. Troost many years since. It being analogous to Holstonia (nobis), I had doubts 

 of its being more than a marked variation. The adult specimen, however, which is 

 figured — received from the Rev. Mr. White — satisfies me that they are distinct species. 

 The figure is made from Mr. White's specimen. The younger specimens of Holstonia 

 have a much closer resemblance than the adults, but the marked difference of the 

 cardinal tooth of the left valve designates the two species. In the Holstonia it is 

 trifid, in the Etowahensis it is single. The outline also is different, the Holstonia 

 being more transverse, and the shell is thicker. In the undulations of the beaks 

 there is also a difference as far as I am able to judge, of the imperfect beaks of the 



two specimens of Etowahensis before me. In the Holstonia these are smaller and 



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