184 NATURAL HISTORY MISCELLANY. 
DISAPPEARANCE OF AURORA IsLanp. — Referring to the state- 
ment of the disappearance of Aurora Island (one of the New 
Hebrides group), recently printed in the newspapers, Mr. Tryon 
exhibited to the Conchological Section of the Academy of Nat- 
ural Sciences of Philadelphia, at their meeting January 5th, 1871, 
two species of shells from the collection, supposed to be peculiar » 
to this island, remarking that in the event of the reported sub- 
mergence of the island being confirmed, these must be classed 
among the lost species. In his report on the mollusca collected 
by Wilkes’s U. S. Exploring Expedition, Dr. Gould gives the fol- 
lowing account of Aurora Island : — 
“ The little island of Metia, or Aurora Island, to the northeast 
ward of Tahiti, is one of peculiar interest. It is a coral island 2 
which has been elevated two hundred and fifty feet or more, an 
has no other high island near it. On it were found four small 
land shells belonging to three genera, viz. :—Helix pertenuis, Heliz 
paratively modern times.” ' 
GEOGRAPHY or THE Sea Bep.— At the meeting of the Royal 
Geographical Society, held on Nov. 29, a paper was read ‘On the 
Geography of the Sea Bed,” by Capt. Sherard Osborn, R. N. The 
author gave an account of our present knowledge of the configura- 
tion of the bed of the ocean, as derived from Admiralty surveys 
and submarine telegraph expeditions during the last fifteen you 
His explanations were illustrated by a number of diagrams shor i 
ing sections of the North Atlantic and other oceans. It hasbeen 
definitely ascertained that the greatest depth of the ocean aan 
~ not reach 3,000 fathoms in any part where telegraphic lines ve i 
been laid. The bed of the North Atlantic consists of two valleys, 
the eastern extending from 10° to 30°, the western from 30° to 50° 
West Longitude. The extreme depth of the eastern valley is under 
13,000 feet, which is less than the altitude of Monte Rosa. THS — 
valley has been traced southward to the equator. It is separated : 
from the western valley by a ridge in 30° West Longitude, in Wi” 
the average depth is only 1,600 fathoms. This ridge termins?” 
to the north in Iceland, and southward at the Azores, 8° that gee 
volcanic in its character at both extremities. Its extreme breadth 
appears to be under 300 miles, and the Atlantic deepens from it of 
