POTAMIDES. 135 



of which is however recurved at the top , which is not 

 the case with P. sulcatus , according to Troschel. In other 

 respects the two species agree in general appearance of 

 the teeth. 



Of my figures fig. 1 represents the central tooth , fig. 1», the 

 same , seen more laterally ; fig. 2 , the lateral tooth in its 

 natural position , fig. 2% the same turned slightly outwards ; 

 fig. 3, the inner marginal tooth, nearly in its natural position, 

 3», the same reversed , 3^^, the same expanded ; fig. 4 , the 

 external marginal tooth , slightly reversed , 4% the same , 

 still more reversed. The figures are magnified about 200 x ; 

 the asterisks indicate the auricles. By the superposition of 

 the teeth it is nearly impossible to observe them sufficiently 

 in their natural position. 



Rhoon, near Rotterdam, June 1894. 



Notes from the Leyden Museum, Vol. XVI. 



