VI.—Archæodiadema, a New Genus of Liassic Echinoidea

Owing to the absence from England of any marine fossils of Triassic age—except the few obscure shells described by Mr. R. B. Newton—the Lias yields the first English representatives of the Neozoic Echinoidea. The fauna is not rich in species, and as a rule the specimens are small; but it is of interest, as its members are primitive in character, and as they foreshadow many of the main lines of evolution followed by the rich Echinoid faunas of the Oolites. Some months ago Mr. Beeby Thompson showed me some specimens from the Upper Lias of Northamptonshire, which form an interesting addition to the primitive types of Liassic Echinoidea; they belong to a new genus, which is the simplest known form of the Diadematinæ, and occupies the same relation to the remaining members of that subfamily that Eodiadema occupies to the Orthopsinæ.