_Voluta elongata; Phorus canaliculatus; Nerinea bisulcata; Pleurotomaria Fleuriausa_, and _P. Santonensis; Natica supracretacea._ ACEPHALA. _Trigonia scabra; Inoceramus problematicus_ and _I. Lamarckii; Clavigella cretacea; Pholadomya æquivalvis; Spondylus spinosus; Ostrea vesicularis; Ostrea larva; Janira quadricostata; Arca Gravesii; Hippurites Toucasianus_ and _H. organisans; Caprina Aguilloni; Radiolites radiosus_, and _R. acuticostus._ BRACHIOPODA. _Crania Ignabergensis; Terebratula obesa._ POLYZOA (BRYOZOA) AND ESCHINODEMATA. _Reticulipora obliqua; Ananchytes ovatus; Micraster cor-anguinum, Hemiaster bucardium_ and _H. Fourneli; Galerites albogalerus; Cidaris Forchammeri; Palæocoma Furstembergii._ 1. POLYPI; 2. FORAMINIFERA; 3. AMORPHOZOA. 1. _Cycollites elliptica; Thecosmilia rudis; Enallocœnia ramosa; Meandrina Pyrenaica; Synhelia Sharpeana_. 2. _Orbitoides media; Lituola nautiloidea; Flabellina rugosa_. 3. _Coscinopora cupuliformis; Camerospongia fungiformis_. Among the numerous beings which inhabited the Upper Cretaceous seas there is one which, by its organisation, its proportions, and the despotic empire which it would exercise in the bosom of the waters, is certainly most worthy of our attention. We speak of the _Mosasaurus_, which was long known as the great animal of _Maestricht_, because its remains were found near that city in the most modern of the Cretaceous deposits. In 1780 a discovery was made in the quarries of Saint Peter’s Rocks, near Maestricht, of the head of a great Saurian, which may now be seen in the Museum of Natural History in Paris. This discovery baffled all the science of the naturalists, at a period when the knowledge of these ancient beings was still in its infancy. One saw in it the head of a Crocodile; another, that of a Whale; memoirs and monographs rained down, without throwing much light on the subject. It required all the efforts of Adrian Camper, joined to those of the immortal Cuvier, to assign its true zoological place to the Maestricht animal. The controversy over this fine fossil engaged the attention of the learned for the remainder of the last century and far into the present.