t 



22 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 13, 14, 58, 59. 



Xairai is a volcanic island, triangular in shape (Plates 12, 14), with 

 sides of about four miles in length. Its central ridge forms an open arc 

 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 b}^ 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- 

 em 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 JSI^ayatha Passage, is studded with 

 rocks and coral patches, undoubtedly the remnants of fragments of the 

 main island, which crop out in everj' direction within the lagoon, and as 

 negro-heads upon the reef flats. Jfaikobu (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 westerh- 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 algae 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. 



