338 BULLETIN 10 0, UNITED STATES NATIONAL MUSEUM 



OBBA MARMORATA (Von Mdllendorff) 



This mollusk was described by Von Mdllendorff as a subspecies of 

 Obbina planulata Lamarck. The large collections in the United 

 States National Museum demonstrate plainly not only that it should 

 be recognized as a distinct species but also that we must recognize 

 a number of zoogeographic races, which are herein defined. 



Obba marmorata varies in shape from broadly conic to depressed- 

 helicoid. The last whorl is obscurely angulated at the periphery, 

 and the last half of the turn has a second obscure angulation between 

 this and the summit, the space between the two being somewhat 

 flattened, while the whorl between the summit and first angulation 

 is well rounded. The postnuclear whorls are marked by rather 

 rough, irregular, and retractively curved incremental lines, which 

 in some of the races almost amount to ribs. In addition to these, 

 the surface is marked by irregular and irregularly spaced impressed 

 lines, which are more or less spiral in arrangement on the early turns, 

 but which on the later whorls assume the form of oblique or zigzag 

 wrinkles. The base is always well rounded and openly unbilicated, 

 the umbilicus being partly closed by the reflected inner lip. The 

 peristome is white, thickened, expanded, and reflected. A tooth is 

 present near the middle of the basal lip. 



The ground color is flesh color, in some with a yellowish tinge, 

 marbled and variegated with brown. There is a tendency, or even 

 a stronger expression in some races, to the formation of a peripheral, 

 superperipheral, and basal spiral band. 



The species ranges from Ilocos Sur south through Benguet, Pan- 

 gasinan, Nueva Ecija, and Kizal Provinces, Luzon, and the smallest 

 race of the species Obba marm,orata ilinensis, new subspecies, comes 

 from the little island Ilin south of Mindoro. 



KEY TO THE SUBSPECIES OF OBBA MARMORATA VON MOIXEN'DORFF 



Periphery of last whorl with a decided angle. 



Greater diameter more than 31 mm bolinaoana 



Greater diameter less than 18 mm benguetana 



Periphery of last whorl without a decided angle. 

 Shell broadly conic. 



Greater diameter more than 35 mm marmorata 



Greater diameter less than 25 mm ecijana 



Shell not broadly conic. 



Shell depressed-helicoid. 



Greater diameter more than 27 mm rizalana 



Greater diameter less than 25 mm ilinensis 



