52 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Naiau. 
Plates 20, 22°, Fig. 1. 
Naiau Island is, like Tuvutha, composed entirely of an elevated lime- 
stone ridge forming a continuous rim round a central depression stated 
to be about 200 feet lower than its highest points, which rise from 530 
to 580 feet above the level of the sea. The sea face of the rim rises 
NORTH POINT OF NAIAU. 
in nearly perpendicular bluffs round the island. At their base they are 
deeply undercut, and the larger fragments are eroded into dome-like 
heads. Off the southeastern point an islet has been isolated from the 
island. Naiau is surrounded by a fringing reef broadest on the eastern 
face, about half a mile wide, where at half tide boats can pass between 
it and the shore, forming an incipient lagoon, and enter through a 
narrow boat harbor passage, out of which, [ am informed by our pilot, 
runs a strong current. There are numerous negro-heads all along the 
outer edge of the fringing reef, especially near the northwestern point of 
the island, where the fringing reef is narrowest. 
Naiau,? Tuvuthé, Kambara, Wangava, and other elevated islands, 
consisting of coralliferous limestone, have been considered to be elevated 
NAIAU, SEEN FROM THE EAST. 
atolls, owing to the existence of a depression in the summit, which is 
looked upon as representing the former lagoon. While that may be the 
1 Moore, Nature, March 18, 1897, p. 463. Others have looked upon these islands 
as extinct craters. 
