When the Challenger's trawl brings up an Ichthyosaurus, along with a few living specimens of Belemnites and Turrilites, it may be admitted that she has come upon a cretaceous "outlier."

Reports to the Admiralty, papers communicated to the Royal Society, and large collections which have already been sent home, have shown that the Challenger's staff have made admirable use of their great opportunities; and that, on the return of the expedition in 1874, their performance will be fully up to the level of their promise.

This is the fact brought out by the Challenger's work, that they have a southern limit of distribution, which can hardly depend upon anything but the temperature of the surface water.