346 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



OBBA LISTERI SIBOLONENSIS, new subspecies 



Plate 88, Figure 2 



The shell is small, depressed-helicoid, with an acute peripheral keel. 

 The nuclear whorls 2, pale brown. The first half of the postnuclear 

 whorls is of the same color as the nuclear turns ; the rest are of buffish 

 tinged flesh-colored ground color, streaked, spotted, and mottled 

 with brown. An ill-defined median interrupted brown band is 

 present on all the turns. The base is of pale buff ground color with 

 a well-developed brown spiral band two-thirds of the distance between 

 the periphery and the umbilicus anterior to the periphery. The de- 

 pressed malleations are also brown and give to the posterior half of 

 the underside of the last whorl a peculiar mottled appearance. The 

 nuclear whorls are marked by rather strong incremental lines and 

 microscopic spiral striations. The postnuclear whorls are strongly 

 keeled at the periphery and the succeeding turns falling below the 

 keel allow this to show as a slender band at the suture. They are 

 marked by strong riblike axial incremental elements and are heavily 

 malleated on the anterior two-thirds between the summit and the 

 suture. In addition to this, fine microscopic spiral striations are 

 present on the spire and also a still finer network of crisscross stria- 

 tions. The basal surface is marked by the continuations of the axial 

 riblike elements and rather strong malleations, which extend from the 

 periphery almost to the umbilical edge. In addition to this, rather 

 strong spiral striations are present, much stronger than those on the 

 upper surface and also the crisscross finer sculpture referred to above. 

 Aperture broadly oval; peristome thickened and reflected, covering 

 one-third of the umbilicus at the parietal wall. 



Type.— The type, U.S.N.M. No. 382924, and five topotypes, U.S. 

 N.M. No. 382925, were collected by C. Canonizado on Sibolon 

 Island off southeastern Mindoro. The type has 4.5 whorls, and 

 measures: Height, 11 mm; greater diameter, 24.7 mm; lesser 

 diameter, 20.3 mm. 



Remarks. — The other five specimens yield the following measure- 

 ments: 



This subspecies can at once be distinguished from all the other 

 members of the Province by the riblike axial sculpture. 



