64 ON THE NAIADES, 



trices confluent ; dorsal cicatrices in the centre of the cavity of the 

 beaks ; cavity of the beaks shallow and tinged with brownish purple ; 

 nacre white anteriorly, thinner and very iridescent posteriorly. 



Remarks. — I owe to the kindness of professor Troost this little 

 species, and name it after an indefatigable naturalist, Mr T. A. Con- 

 rad. It belongs to that group which is distinguished by an imma- 

 ture hinge, and which I have noticed in my remarks on the U. Hil- 

 drethius. The U. Conradius certainly resembles that shell closely. It 

 is, however, less cylindrical, and has the teeth more perfect. It also 

 has rays and undulations which I have not observed on the other. In 

 outline it more closely resembles the U. iris (nobis), but differs in the 

 teeth and in the rays. Having but two specimens of this species to 

 examine, some of the characters may be found to differ in other speci- 

 mens. One of these is slightly emarginate at the basal margin. 



Unio divaricatus. Plate IX. fig. 24. 



Testa ellipticd,transversd, subcompressu, valde iricequilateru ; valvidistenuibus ; 

 nutibvs plicis pulchris divaricatis ; dentibus cardinalibus parvis, compressis ; 

 lateralibus longis et subtenuibus ; margaritd alba et iridescente. 



Shellelliptical, transverse, rather compressed, very inequilateral ; valves thin; beaks 

 with beautiful divaricating folds ; cardinal teeth small, compressed ; lateral teeth long 

 and rather thin ; nacre white and iridescent. 



Hab. Egypt. Duke de Rivoli. 



My Cabinet. 

 Diam. -5, Length -9, Breadth 1-4 inches. 



Shell elliptical, transverse, somewhat compressed, very inequilate- 

 ral : substance of the shell thin ; beaks covered with beautiful folds 

 diverging from their apex; ligament rather short and slender; epi- 

 dermis greenish, smooth ; cardinal teeth small, compressed, double 

 in the right valve, and single in the left ; lateral teeth long, rather 

 thin and nearly straight ; anterior cicatrices slightly confluent ; pos- 

 terior cicatrices confluent ; dorsal cicatrices situated in the centre of 



