In this paper I purpose giving a history and description of the Cretaceous group of Aporrhaïs, as far as they are at present known to me, especially of those forms which are so beautifully preserved in the Gault of Folkestone, and so-called Upper Greensand of Blackdown. I regret that I cannot include the Aptien and Neocomien species, but the collections at present open to me are too meagre to give anything like a complete account of them. In the whole group there are even now many points which require further research; the correlation of some of the forms with those on the Continent is still unsatisfactory, from the difficulty experienced in comparing actual specimens. The figures available, even in the most modern works, appear in some cases to have been restored, and not therefore to represent the form of any shell that has been really met with.