Many of the living forms of Cephalopodous molluscs are now, thanks to the Brighton Aquarium, familiar to us all; and, as the habits and characteristics of the squids, octopods, and cuttles have been duly recorded by Mr. Henry Lee in his amusing book on “The Octopus,” published in 1875, I shall here restrict myself to those points in the structure of the living forms which bear upon the history of the class as a whole, giving merely those anatomical details which are absolutely indispensable for a right comprehension of the nature and affinities of the numerous fossil and extinct members of the order. I may, however, observe, en passant, that the existence of a certain sub-stratum of truth in the old stories of giant Cephalopods was ably proved by Mr. Saville Kent, in the “Popular Science Review,” for 1874, and that specimens have been more recently cast ashore in Trinity and Logie Bays, on the coast of Newfoundland, that may fairly claim to be of enormous dimensions. Thus, in a truly formidable calamary, or squid, the tentacular arms measured 30 feet, the largest suckers being one inch in diameter, the shorter (or pedal) arms were 11 feet long, and the body was 10 feet. Professor Verrill has also described a huge cuttle, estimating the total length at 40 feet, the large tentacles were 26 feet long, with a maximum circumference of 16 inches at their union to the body. A new genus of calamary, allied to the Architeuthis of Steenstrup, with arms measuring over 23 feet, was discovered on the island of St. Paul, in the Indian Ocean, by M. Charles Vélain, the naturalist attached to the French Expedition for the observation of the transit of Venus, at that station. The size attained by some of the fossil species will be noted in the sequel.