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Excerpt from A Monograph of the British Fossil Trigoniæ Throughout the great Mesozoic epoch there are, perhaps, no testaceou's forms, with the exception of the Ammonites, of importance superior to the Trigonias, or which demand from the Palaeontologist more careful discrimination and more extensive acquaintance with their various aspects, to enable him to overcome the difficulties that meet him when he attempts their certain determination. The importance of the genus is based upon its great stratigraphical range, its world-wide occurrence, its great diversity of aspects, locally also by its individual numbers. Its prominence and distinctness as a. Genus immediately arrests the attention Of the observer, and, notwithstanding the diversity of its aspects, a Trigonia is a form recognised without difficulty even by a tyro. The generic characters are so well known that to give a minute description of them would amount to a mere useless repetition of that which has been so fully accomplished by Agassiz and by other Palaeontologists. I prefer, therefore, to allude to them with the greatest possible conciseness, and will adopt the terse and brief definition given by my late lamented friend, Dr. S. P. Woodward, in his well-known 'manual of the Mollusca Shell thick, tuberculated, or ornamented with radiating or concentric ribs; posterior side angular, ligament small and prominent; hinge-teeth 2 - 3, diverging, transversely striated centre tooth of the left valve divided; pedal impressions in front of the posterior adductor, and one in the umbo of the left valve; anterior adductor impression close to the umbo. Shell almost entirely nacreous, and usually wanting or metamorphic in limestone strata. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the wor