DUTCH BORNEO-EXPEDITION. 161 



Locality : Mandai River near Nanga Kalis, February 1894 

 (Büttikofer). 



This shell is very different from any Bornean species. 

 It has a remote resemblance with U. delphinus Gruner , 

 but that species is still more elongated, much more winged 

 and less inflated. 



41. Unio infrarostratus , u. sp. 

 (Plate 4, fig. 2). 



Shell oval, much inflated, very inaequilateral , rather 

 smooth , with only slight wrinkles and numerous fine 

 concentric striae ; umbones rather prominent, decorticated ; 

 epidermis dark brown with a metallic lustre , somewhat 

 velvety near the extremities ; upper margin slightly curved 

 posteriorly, straight anteriorly ; anterior margin rounded , 

 passing insensibly in the convex ventral margin ; posterior 

 margin oblique above, with an obtuse angle near the 

 superior one ; somewhat below the middle of its length 

 it is suddenly bent inwards and then outward again , 

 forming a sinus, in the lower part of which the shell is 

 angular ; the margin is then nearly straight and runs with 

 an angle into the ventral one; from these two angles of 

 the margin, obtuse angles run towards the umbones. 



Nacre blue , iridescent near the free margins , olive yel- 

 low near the umbones ; hinge strong , teeth irregular , 

 thick , a crenulated one in the right , two nearly consoli- 

 dated ones in the left valve ; 2 lamellae in the left , one 

 in the right valve ; they are well developed, nearly straight. 

 Anterior scars irregular, deep, posterior ones shallow, pallial 

 line distinct. 



Long. 67, alt. near the umbones 41 , about the middle 

 of the posterior side 47 mill. ; diam. 29 mill. 



Locality: Small brook near Singangi in the Ketoengau 

 District (Moret). 



This species may be distinguished from the other known 

 Bornean species by its posterior margin , and it is easily 



ISotes from tbe Leyden ]Museu.na, Vol. XVII. 



11* 



