A Letter from Mr. Emanuel Mendez da Costa, F. R. S. to the Rev. Thomas Birch, D. D. Secr. R. S. concerning the Fossil, Found at Dudley in Staffordshire, and Described in the Phil. Trans. N. 496

XLII. A Letter from Mr. Emanuel Mendez da Costa, F. R. S. to the Rev. Thomas Birch, D. D. Secr. R. S. concerning the Fossil, found at Dudley in Staffordshire, and described in the Phil. Trans. N. 496. SIR, Read July 12, 1753. THE famous fossil, which Dr. Lyttelton shew'd to the Royal Society some time ago from Dudley in Staffordshire, and which is engraved and described in No. 496 of the Transactions, caused many arguments to what class of animals it belonged. Dr. Pococke afterwards produced two or three specimens of it extended, which proved it of the crustaceous tribe of animals. But none of his said specimens being very fair, I have taken the liberty to send you a very fair specimen of the said fossil extended, sent me last week from the iron mines at Colnbrookdale in Shropshire, and which absolutely determines me to pronounce it to be the remains of a crustaceous animal, of that kind called Pediculi marinini, which are scaled all round, and can at will roll themselves up: And this particular kind (not to my knowledge yet discover'd from sea) may be justly synonymed Pediculus marinus major trilobos. Tho' I heretofore thought it not described by any English author, yet I find it is described and figured, tho' badly, by our late member Mr. Edw. Lhuyd, in his Lithophylacium Britannicum Ichnographia, Epist. i. p. 96. Table XXII. who found them in plenty plenty in quarries, juxta ædes nob. v. D. Gryfidii Rice de Newton, arm. prope oppidum Sancti Teilavii, in comitatu Mariduniaæ. He calls it Buglossa curta stri-gosa. He also gives the figure of it without any description, in the Phil. Trans. No 243. I beg you would communicate this supplement to the Royal Society in my name. I remain, with great esteem, SIR, London, July 12, 1753. Your very humble servant, Emanuel Mendez da Costa. XLIII. Letters relating to a Theorem of Mr. Euler, of the Royal Academy of Sciences at Berlin, and F. R. S. for correcting the Aberrations in the Object-Glasses of refracting Telescopes. I. A Letter from Mr. James Short, F. R. S. to Peter Daval, Esq; F. R. S. Dear Sir, Read April 9, 1752. THERE is published, in the Memoirs of the Royal Academy at Berlin, for the year 1747, a theorem by Mr. Euler, in which he shews a method of making object-glasses of telescopes, in such a manner, as not to be affected by