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BULLETIN 120, UNITED STATES NATIONAL MUSEUM. 



which gave rise to P. fliformis and P. tenuis. The occurrence of 

 the two almost identical species, one on each side of the Bali-Lombok 

 line, shows this group also to be an ancient one, pre-Eocene (fig. 

 236), altliough the elongated form of its species is doubtless 



secondary and might have led us to regard the origin of the group 

 as more modern. The presence of one species in the northern and 

 western Malay Islands, including Formosa, would date the origin 

 of the group either in the Jurassic (fig. 233), and so a period earlier 



