92 UNIO NIEUWKNHUIS!. 



NOTE XV. 



DESCRIPTION OF A NEW UNIO FROM BORNEO 



BY 



M. M. SCHEPMAN. 



Plate i. 

 Unio Nieuioenhuisi , n. sp. 



Shell somewhat squarely oblong, moderately inflated, very 

 inaequilateral , covered with a dark-brown fibrous epidermis, 

 giving to the shell the appearance of being concentrically 

 striated; striae coarser towards the margins, if seen by 

 transparent light the colour is yellowish-brown. The um- 

 bones being decorticated , no sculpture is perceptible on 

 these parts, but the posterior slope is provided with radia- 

 ting folds, usually becoming bifurcate towards the margin. 

 Upper margin moderately curved, anterior margin rounded, 

 passing insensibly into the rather straight ventral margin ; 

 posterior margin sinuous above, then abruptly truncate, 

 forming two angles, one at the upper part of the trunca- 

 tion and one at the beginning of the ventral margin; from 

 this point an obtuse ridge runs towards the umbones. Nacre 

 iridescent, bluish white near the margins , olive yellow near 

 the umbones. Hinge strong, one thick tooth in the right 

 valve , with crenated edge , two in the left valve , the 

 posterior one being the largest; both are obsoletely crenated. 

 One lamella in the right valve, two in the left one, they 

 are slightly curved, somewhat crenated posteriorly. An- 

 terior scars irregular, deep, posterior ones shallow, pallial 

 line distinct. A flat callosity runs from the umbones, obli- 

 quely towards the ventral margin. 



Long. 69, alt. near the umbones 37, at the angle of 

 superior and posterior margin 40, diam. 19 mill. 



Locality: Bloe-oe, east Borneo (Dr. Nieuwenhuis). 



This interesting novelty may be easily distinguished from 

 the known Bornean species , by its strongly sculptured 

 posterior slope ; this character is only present in Unio 

 radulosus Drouet and Chaper, which is however in nearly 

 every other respect quite different. I have named the species 

 in honour of its discoverer. 



Rhoon near Rotterdam, March 1898. 



Notes from the Leyden. ]Museum , Vol. XX. 



