From Delambre we proceeded to the Montebello Islands, principally in order to set at rest two points of great interest, namely, the position of Ritchie's Reef, and of the long lost Tryal Rocks. On the 31st, in the afternoon, we anchored in 6 fathoms on the eastern side of Tremouille Island, a cliffy islet off the south-east end of which bore South 42 degrees East two miles. The tide was ebbing and setting to the North-North-East two knots an hour. We found the Montebello Group to be confined by a coral reef encircling it. The two principal islands are Tremouille and Hermite Islands. The fact that these and their neighbours are not separated in the charts fully evinced the necessity of our visit. Leaving a boat to examine them, the ship proceeded towards the northern end of Barrow's Island, being anxious to avoid the southerly winds to which the anchorage off Tremouille is exposed. These usually commenced at midnight, blowing from south-west, freshening and veering to south by 8 A.M., and by about 10 moderating at South-South-East. On our way to Barrow's Island they were so violent as to cause the ship to drive with two anchors ahead, there appearing to be no holding ground, but simply a coating of sand over a rocky ledge. During the prevalence of these winds the temperature varied from 66 to 76 degrees. Near Barrow's Island, on our passage, I shot (from the quarter-boat) the largest sea-snake ever killed. It is figured and described in the Appendix, by Mr. J.E. Gray, as Hydrus major, and measured eight feet one inch in length, by three inches broad; the colour was a dark yellow: several smaller ones striped brown and white were also seen. BARROW'S ISLAND.