The marine deposits of the miocene epoch show the remains of extinct genera of dolphins (Ziphius and Dioplodon) and of whales (Balcenodon). Petrified cetaceous teeth and ear-bones, called " cetotolites " (fig. 107) have been washed out of vious strata into the red crag of Suffolk. These fossils belong to species distinct from any known existing Cetacea, and which, probably, like some temporary quadrupeds, retained fully-developed characters which are embryonic and transitory in existing cognate Mammals. The teeth of these Cetacea were determined in 1840, the ear-bones in 1843. The vast numbers of these fossils, and the proportion of phosphate of lime in them, led Professor Henslow* to call the attention of agricultural chemists to the red crag as a deposit of valuable manure. Since that period it has yielded a large supply, worth many thousand pounds annually, of the superphosphates. The red crag is found in patches from Walton-on-Naze, Essex, to Aldbro', Suffolk, extending from the shore to 5 or 15 miles and more inland. It averages in thickness 10 feet, but is in some places 40 feet. Broken-up septarian nodules form a rude flooring to the crag, left by the washing of of the London clay, and called " rough stone." The phos phatic fossils, or " cops" as they are now locally termed, occur in greatest abundance immediately above the " rough-stone." Thousands of cubic acres of earlier strata must have been broken up to furnish the cetacean nodules of the " red crag." This is a striking instance of the profitable results of a seem ingly most unpromising discovery in pure science,—the deter mination of what in 1840 was regarded as a rare, unique, and most problematical British fossiLt Our knowledge of the progression of mammalian life dur ing the miocene period is derived chiefly from continental fossils. These teach us that one or two of the generic forms most frequent in the older tertiary strata still lingered on the earth, but that the rest of the eocene Mammalia had been superseded by new forms, some of which present characters intermediate between those of eocene and those of pliocene genera. The Dinotherium, and narrow-toothed Mastodon, for example, diminish the interval between the Lophiodon, and the elephant ; the A naracotherium. and Hippohyus, that between Chceropotamus and Hippopotamus ; the Accrotherivm was a link connecting Palceotherium with Rhinoceros ; the Hippo therium linked on Paloplotherium with Equus.
One of the most extraordinary of the extinct forms of the cetaceous order has been restored from fossil remains dis covered in formations of the miocene age in Europe and North America. The teeth of this carnivorous whale, for which the generic name Zeuglodon seems now to be generally accepted, were first described and figured by the mediaeval pala‘ontolo gist Scilla, in his treatise entitled De Corporibus Marinis (4to, 1747, tab. xii., fig. 1), and have since given rise to various interpretations. The originals were obtained from the miocene strata at Malta, and are now preserved in the Woodwardian museum at Cambridge.
The remains of a gigantic species of the same genus, covered by Dr. Harlan in miocene formations of Arkansas, Mississippi, were described and figured by him as those of a reptile, under the name of Teeth of a smaller species, discovered by M. Grateloup, in miocene beds of the Gironde and Herault, were ascribed by him also to a reptile, under the name of lodon4 In 1839 Dr.
lan brought over his cimens of Basilasaunts to London, and ted them to the writer's inspection, by whom they were determined to be mammalian and cetaceous. The entire skeleton has since been obtained from miocene deposits in Alabama, revealing a length of body of about 70 feet. The skull is very long and narrow ; the nostril single, with an upward aspect., above and near the orbits. The jaws are armed with teeth of two kinds, set wide apart ; the anterior teeth have subcompressed, conical, slightly-recurved, sharp-pointed crowns, and are implanted by a single root ; the posterior teeth are larger, with more compressed and longitudinally extended crowns (fig. 108), conical, but with a more obtuse point, and with both front and hind borders strongly notched or serrated. The crown is contracted from side to side in the middle of its base, so as to give its transverse section an hour-glass form (fig. 109), and the opposite wide longitudinal grooves which produce thj form become deeper as the crown approaches tip socket, when they meet and divide the root into two fangs.
The name Zeu glocion (yoke-tooth) refers to this structure. The mode of suc cession of the teeth in this genus conforms to the general mammalian type more than does that of any of the existing carnivorous Cetaceans. In the figure given by Dr. Carus* of a portion of the jaw of Zeuglodon cetoide8, a deciduous molar (fig. 108, a) is about to be displaced and succeeded, vertically, by a second larger molar. This mode of succession is not known in the Platanigta or Inia, which among existing true Cetacea present teeth most like those of Zeuglodon; but it is a mode of succession and displacement affecting certain teeth in the herbivorous Cetacea, or Sirenia ; and we thus seem to have in the Zeuglodon another of those numerous instances of a more generalized character of organization in older tertiary Main malia. In systematic characters, Zeuglodon typifies a distinct family or group, intermediate between Cetacea proper and Sirenia.
Of the latter family or order, however, represented at the present day by the Dugongs, Manatees, and Stellerians or Arctic Manatees (if the species still survives), there were abundant and more widely distributed representatives during the miocene period, having, upon the whole, the nearest affinity with the existing African Manatee (Manatus Senega lensis), but with associated characters of the Dugong (Halicore). There were, e. g., two incisive tusks in the upper jaw, and four or five small incisors along the deflected part of each ramus of the lower jaw. The upper molars, with three roots, were thickly enamelled, like those of the Manatee, but with a pat tern of grinding surface which led Cuvier to attribute detached specimens to a small species of Hippopotamus. The lower molars had two roots. All the bones have the dense or solid structure of those of the Sirenia. On the remains of this remarkable amphibious Mammal, discovered by Kaup in 1838, in the miocene beds at Eppelsheim, he founded the genus Hali therium. Other remains have been discovered in Piedmont Aste, and many parts of France, from the " c,alcaire grossier" of the Gironde, containing Lophiodont fossils, up to the plio cene near Montpellier ; at which period the Halitherium seems to have become extinct.