So little is known of the extension through later Mesozoic deposits of Selachian teeth belonging to the familiar type of Acrodus, as represented in the Lias, that any additional evidence upon the subject is invested with considerable interest. It is impossible, of course, from these isolated relics, to determine whether the original Sharks were as closely allied as the resemblances in their dentition might at first lead one to suspect;inone case, indeed, it has been proved that the complete fish differs much from the Liassic species; but the persistence of the dental type is at any rate of some significance, and it may therefore be acceptable to offer a few notes upon the undescribed Jurassic and Cretaceous Acrodonts preserved in the British Museum. These specimens furnish evidence of at least two new specific modifications, and they are also suggestive of novel points in regard to some of those already known.