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2 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
lagoon of pale green water, the sea breaking heavily upon the edges. I 
consider this reef as having been denuded and eroded to its present stage, « 
which precedes that of a more sunken atoll, like Adolphus Reef, with a 
deeper lagoon. 
Nairai. 
Plate 11%, Fig. 4, and Plates 12, 14, 58, 59. 
Nairai is a volcanic island, triangular in shape (Plates 12, 14), with 
sides of about four miles in length. Its central ridge forms an open are 
to the east, its central peak rising to a height of over eleven hundred feet 
The western slope of the island is much less steep than the eastern side. 
(Plate 58.) The island is edged by a narrow fringing reef, with the 
exception of the most western point, where it expands into a broad 
fringing reef, the outer patches of which extend into the outer encircling 
reef. The encircling reef surrounding the island is a narrow reef flat, 
from a quarter to a mile distant from the eastern side, and from one to 
one and a half on the western side. But the prolongations of the horns 
of the outer reef to the northeast, south, and west are from four to five 
miles distant, forming thus three lagoons separated by long passages. 
(Plate 14.) The greatest depth in the lagoons is twenty-six fathoms off 
one of the western passages. The general depth is from ten to fifteen 
fathoms. The inner edge of the eastern outer reef is fringed with coral 
patches. This part of the reef is continuous, having only one boat 
entrance nearly opposite the southern extremity of the island. The 
western reef has two deep passages, and a boat passage near the south- 
ern horn of the atoll. This as well as the other points of the outer 
reef, both at the northeastern and northwestern horns, are studded with 
coral patches. The greater part of the lagoon, extending from the 
northern part of the island to the Nayatha Passage, is studded with 
rocks and coral patches, undoubtedly the remnants of fragments of the 
main island, which crop out in every direction within the lagoon, and as, 
negro-heads upon the reef flats. Naikobu (Plate 59), or Magnetic Island, 
a small island to the south of Nairai, is one of these outlyers; it is 
ninety feet in height, the base running into ten fathoms, and is covered 
with corals. It is further remarkable for the great variation it causes 
to the compass. We observed on the top a westerly deflection of 87°. 
The bottom of the lagoon consists of fine coral, coralline sand, and broken 
shells, which form large white areas separating the coral patches and 
the numerous patches of coralline alge which flourish upon the floor of 
this lagoon wherever we examined it. The corals of the fringing reefs 
of both Nairai and Ngau were growing specially vigorously. 
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