fiR ])ESCRIPTIONS OF 



probably over the whole of it. On the side they are nearly perpendicular, but on the 

 posterior slope they are oblique, and as they join on the umbonial slope they make 

 an angle there of nearly 90°. The folds are quite observable in the nacre of the 

 interior. The rays on the posterior jDortion are very distinct, of a dark green, and 

 so broad on the umbonial slope as to give it a dark greenish hue. The transverse 

 striae are very well marked, almost amounting to sulcations. A marked characteristic 

 of this species is, that the double cardinal tooth is in the right valve and the single one 

 in the left. 



UnIO MUTABILIS. PI. 38, fig. 127. 



Testa liBvi, late elliptica, subcouipressa, vald6 iusequilaterali, ad basiin subrecta ; valvulis tenuibus, antice 

 crassioribus ; natibus prominulis, ad apices undulatis, feve terminalibus ; epidermide castanea, nitida 

 et eradiata; dentibiis cardinalibus parvis, in utroque valvulo duplicibus ; lateralibus praelongis sub- 

 curvisque ; margaritu cjcruleo-alba et valdi" iridesceiite. 



Shell smooth, widely elliptical, compressed, very inequilateral, nearly straight at 

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

 and nearly terminal ; epidermis chestnut brown, shining and without rays ; cardinal 

 teeth small and double in both valves ; lateral teeth very long and slightly curved ; 

 nacre bluish white and very iridescent. 



Unio mutahiUs, Lea. Proc. Acad. Nat. Sci., 1859, p. 152. 



Hah. — Brisbane water, Australia, New Zealand. H. Cuming; and Murray river, 

 Australia. W. Newcomb, M. D. 



My cabinet and cabinets of Mr. Cuming and Dr. Newcomb. 

 Diam. -5, Length 1, Breadth 2-1 inches. 



Shell smooth, widely elliptical, compressed, very inequilateral, nearly straight at 

 the base ; substance of the shell thin, thicker before ; beaks a little prominent, with 

 radiate undulations at the tips and nearly terminal ; ligament rather long, thin and 

 reddish ; epidermis chestnut brown, shining, with distant marks of growth ; umbonial 

 slope raised and rounded ; posterior slope compressed and raised into a keel ; cardinal 

 teeth small and double in both valves;, lateral teeth long, acicular and slightly 

 curved ; anterior cicatrices confluent, as regards the lower one, but distinct from the 

 upper one ; posterior cicatrices confluent ; dorsal cicatrices in a row jjosterior to the 

 centre of the cavity of the beaks ; cavity of the shell rather shallow ; cavity of the 

 beaks scarcely observable ; nacre Wuifh white and very iridescent. 



Remarks. — I have four specimens of this shell before me. Three from Mr. Cuming 

 and one from Dr. Newcomb. They are of three different ages and have quite dissimilar 

 aspects. The oldest is from Brisbane Water and is three inches wide. The nacre is 

 much thickened, the epidermis blackish and the beaks greatly eroded. The next 

 age is from New Zealand, is two and one-quarter inches wide and is in nearly a perfect 

 condition. This is the one figured, and the description is made from it. The two 



