The animals, either wholly new, or new to Britain, described in the following communication, were taken during a yachting cruise, with our indefatigable friend Mr Macandrew, among the Hebrides, in the month of August 1850. During this voyage, which lasted three weeks, a series of observations were conducted by means of the dredge and the towing-net. Not a single new form of testaceous mollusk was procured; our exertions were amply rewarded, however, by the discovery of several remarkable Ascidians and Radiata, some of them so curious in themselves, and so important in their zoological bearings, that we have thought it desirable to lay an account of their characters and anatomy before the Royal Society of Edinburgh.