260 UNIO MISOOLENSIS. 



regularly curved above, rounded below and running with 

 a very obtuse angle at the umbonal ridge , which is rather 

 obtuse , into the ventral margin*. Ligament long , narrow , 

 yellowish-brown. 



Nacre bluish white, more iridescent near the posterior 

 part, brownish near the umbones; scarcely more than one 

 short, thick, crenated tooth in each valve; a small knob 

 in the left valve may perhaps be considered as a second 

 tooth; lateral lamellae: 2 in the left valve , one in the right 

 one; they are elongated, slightly curved, rather thick. 



Anterior scars : a large rounded one , which is rather 

 deep, and a much smaller, very deep one, just below the 

 tooth; posterior scars very shallow; pallial line distinct. 

 Nacre much thickened near the antei'ior part of ventral 

 margin, forming a callus, which is connected with another 

 callus , running from the umbones to this ventral one. 



Long 65, alt. near the umbones 24, diam. 16 mill. 



Locality. Misool (Hoedt). — In the collection of the 

 Ley den Museum. 



The nearest ally of this Unio , amongst the known spe- 

 cies of the same geographical region , may be Unio Bec- 

 c.arianus Tapp. Cauefri, or its variety a, but it diifers in 

 shape and sculpture ; the anterior margin in that species 

 is not protruded below, the posterior part is much more 

 elongated and acuminated in Beccarianus , and the line 

 from the ligament to the posterior end is much straighter, 

 while it is curved in the new species. 



Rhoon near Rotterdam, February 1897. 



Notes from the Leyden M.useuixi, "Vol, XVIIl. 



