102 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
summit of a peak of elevated coralliferous limestone, which have been 
denuded to the level of the sea and then subjected to submarine erosion, 
forming first a flat, then an incipient atoll of which the lagoon has been 
gouged out, in one case to twelve, in the other to sixteen fathoms. 
Upon the outer edge of the flats, corals have grown, protecting the rims 
to a great extent from further denudation and erosion. 
The depth of the plateau from which Tova rises is probably very 
considerable. The depth of water at a distance of seven or eight miles 
is, judging from soundings to the eastward, perhaps as much as 1,200 or 
1,500 fathoms ; while Thakau Momo apparently rises from a shallower 
depth of less than 500 fathoms to the north, and about 900 fathoms at 
a distance of about five miles. 
Such atolls as Thakau Momo, Tova, and a host of others occurring in 
Fiji, are identical in their mode of formation with such an atoll as the 
Hogsty in the Bahamas,’ the lagoon of which I believe to be due to 
mechanical causes similar to those which have shaped the above named 
Jagoons in Fiji. While the former are recognized by writers on coral 
reefs as true atolls, the latter are regarded as pseudo atolls. It is juggling 
with words to represent structures as different because the one is in the 
Pacific and the other in the Atlantic, and because the one is in an area 
recognized as stationary or as one of elevation, while the other is in an 
area formerly supposed to be one of subsidence and which is now found 
to be one of elevation. In both cases the coral rims of the atolls are 
shown to be of little thickness. The same authors refuse to recognize 
as true barrier reefs, and call them patch reefs, barrier reefs occurring 
in other districts than those examined by Dana and Darwin, because 
they have been shown to be of comparatively moderate thickness. We 
can now show, in the very districts which have been selected as typical, 
that neither the coral reefs of the atolls nor those of the barrier reefs 
have the thickness attributed to them. 
Thakau Lekaleka. 
Plates 21, 111. 
On our way from Oneata to Mothe we steamed: close to Thakau 
Lekaleka (Plate 21), a very narrow reef flat of polygonal outline, some- 
what more than a mile in diameter, enclosing a shallow lagoon, judging 
from the light blue color of the impounded water. The reef flat rises 
1 Bull. Mus. Comp. Zoél., Vol. XX VI. No. 1, p. 103, 1894, 
