﻿AND SPECIES OF THE FAMILY UMONIM3. 305 



biangular behind, flattened on the sides ; substance of the shell rather thick ; beaks a 

 little prominent and placed towards the anterior margin ; posterior slope raised into a 

 carina ; ligament thin, long and nearly straight ; epidermis blackish brown, shining 

 on the umbonial slope ; furrows deep on the anterior portion, nearly obsolete on the 

 umbonial slope ; umbonial slope rounded and but slightly raised ; cardinal teeth very 

 small, in the left valve single, triangular and elevated into a sharp point, in the right 

 valve double, the superior division being very small ; lateral teeth very long, lamellar, 

 and but slightly curved ; anterior cicatrices distinct ; posterior cicatrices confluent ; 

 dorsal cicatrices consist of a long row from the smaller anterior cicatrix across the 

 interior cavity to the under part of the lateral tooth ; cavity of the shell rather shal- 

 low ; cavity of the beaks small, subangular ; nacre purple and iridescent. 



Remarks. — But a single specimen of this shell is before me ; interesting from the 

 fact, as an Australian species, it should so closely resemble an American one, as, at 

 first sight, it might be considered to be merely a variety. It has very nearly the 

 exact outline of Hopetonensis, (nobis,) from Georgia, and is nearly of the same color 

 in the epidermis. It differs in having transverse furrows nearly over the whole disk, 

 which in the Georgian are but slightly developed. It has smaller teeth, and in the 

 left valve the cardinal tooth is single, in the right scarcely bifid. The color of the 

 nacre of the specimen before me is of a darker purple than any of the Georgian species 

 which I have seen. The color of the nacre may differ in other specimens, as it does 

 in the Hopetonensis, which is sometimes white and sometimes slightly salmon colored. 

 The beaks of the specimen of Shuttleworthii before me are eroded, and therefore it is 

 impossible to say if they be undulate ; but I suspect that in perfect specimens they 

 will be found to be so, as on the posterior slope very indistinct undulations may be 

 perceived, decussating an obscure furrow running from the beaks to the posterior 

 margin. If in other specimens these folds are found more numerous and more pro- 

 nounced, then we ought to remove the species from the furrowed to the plicate group. 

 The carina is so much elevated that it might almost be considered to belong to the 

 alate division. 



Unio Dunkerianus. PI. 28, fig. 20. 



Testa plicata, transversa, subinflata, valde insequilaterali, postice obtuse angulata ; valvulis subtenuibus ; 

 natibus prominulis, costis divaricatis ; epidermide tenebroso-fusca politique; dentibus cardinalibus 

 longis compressisque ; lateralibus prselongis, lamellatis rectisque ; margarita casruleo-alba et valde 

 iridescente. 

 Shell folded, transverse, somewhat inflated, very inequilateral, obtusely angular 

 behind ; valves rather thin ; beaks with diverging ribs ; epidermis blackish brown 

 and polished ; cardinal teeth long and compressed ; lateral teeth very long, lamellar 

 and straight ; nacre bluish white and very iridescent. 

 Proc. Acad. Nat. Sci. Vol. N, p. 04. 



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