96 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
towards the south off the west coast, and on the eastern face of the 
island it attains a width of nearly a mile. In continuation of the 
fringing reef off the northern face and off the southern spit of Lakemba 
extends a narrow outer reef, enclosing a lagoon, irregularly rectangular 
in shape, about five miles in length. The lagoon is thickly studded 
with patches and heads; its greatest depth is 14 fathoms; on the east 
face of the outer reef there is a passage for steamers. This is another 
exception of a lagoon entrance on the windward side. It should, how- 
ever, be noted that the east face of the Lakemba atoll is protected to 
some extent by Aiwa and Oneata. 
The resemblance in shape of Lakemba and Kanathea, the latter of 
which we did not visit, is very marked. The encircling reef of the latter 
surounds a larger lagoon ; there is also a narrow extension of the lagoon 
on the south side of Kanathea, and a boat passage on the east face. 
One mile and a half south of Kanathea, and separated from it by a 
channel with a depth of 131 fathoms, lies the small summit of Morse 
Reef; and off the central part of the northern face of the encircling 
reef, Boehm Rock. At Lakemba Gardiner? has noticed the flat lime- 
stone hills which rise abruptly to a height of 60 to 70 feet on the west 
coast. the foundation being volcanic conglomerate, which forms the rest 
of the island. Captain Wilson states that on the reefs of the extreme 
south some of the islets are limestone, others volcanic, and he considers 
the three larger islands in the centre to be the remnants of an old 
crater. 
Thithia. 
Plate 20. 
I am informed by Bishop Vidal of Levuka that the island of Thithia, 
which we did not visit, is also composed in part of elevated limestone, 
in which large caverns have been excavated similar to those we saw in 
Ngillangillah Island. It is also stated by others to be in part volcanic. 
It resembles Mango in outline, appearance, and structure, but is some- 
what smaller; the fringing reef surrounding it is narrow. The central 
part of the island is probably a volcanic ridge, which has elevated the 
ancient limestone surrounding it. 
1 Loc. cit., p. 466. 
