III.—Studies in Edrioasteroidea III.— Leretodiscus, n. g. for Agelacrinites Dicksoni, Billings

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The specimen herein to be considered is one of great historical interest, for it was the first specimen of an Edrioasteroid made known to science. It was discovered by Dr. J. J. Bigsby in limestone now recognised as of Lower Trenton age, forming Table Rock at the Chaudière Falls on the Ottawa River at Ottawa (then called Bytown). Canada, in 1822. Brought by Bigsby to England, it was figured and described, though not named, by G. B. Sowerby in 1825. E. Forbes, who had the speciman for study, referred to it in his memoir “On the Cystideæ of the Silurian Rocks of the British Islands,” since the “aspect” of his Agelacrinites Buchianus “immediately called [it] to mind”; he even went so far as to say that there could “be no question … of its being generically allied” to that species. Considering the not unnatural inadequacy of Sowerby's description and figure, the reputation that Forbes had as an authority on echinoderms, and the comparative imperfection of the first found specimens of Edrioaster, it was not surprising that E. Billings in 1856 should have supposed a new Trenton fossil, undoubtedly congeneric with Agelacrinites Buchianus, to be of the same species as that found by Bigsby and should therefore have applied to it the trivial name ‘Bigsbyi,’ while giving to a fossil of obviously different structure the name ‘Agelacrinites Dicksoni.’ In February, 1858, Billings travelled to London with the fossils in question, and found that Bigsby's specimen was not, after all, the same as his Cyclaster Bigsbyi, but was specifically identical with his A. Dicksoni. He redescribed the species, and had his type-specimen, as well as Bigsby's fossil, figured by C.R. Bone.