Proceedings of the Dorset Natural History and Antiquarian Field Club Volume 11 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1890 edition. Excerpt: ...shining ganoid scales, composed of two layers, the inferior bone, and the upper enamel; they are placed edge to edge in oblique rows. In the older forms there are no vertebral centra, and the skull, which is cartilaginous, is protected by plates, whereas in the later forms the margins of the vertebrae are either ossified or have osseous rings enclosing the primitive matter of the notochord. Some, however, are similar to the Teleosteans. The gills are free and protected by an operculum. The majority of the fossil ganoids belong to the Palaeozoic and Mesozoie age, and are only scantily represented now, the sturgeon being one; the ganoid-plates are united into a shield over the head, but are detached over the body; the mouth is not furnished with teeth; the tail is heterocercal. The sub-order, Acipenseroidei, to which the Sturgeon belongs, is not known with certainty to have come into existence before the Eocene age, when it is represented by the Acipenser toliapicus of the London clay. The living ganoids are, for the most part, inhabitants of fresh waters; but many of the extinct forms are associated with marine animals, therefore they probably inhabited the sea. The Order Teleostei includes the great majority of the fish of the present day. The skeleton is partially ossified, distinct cranial bones and a lower jaw. The osseous column consists of completely ossified vertebrse, hollow at both ends, amphiccelous, the tail symmetrical. The last vertebra has a central position in the base of the fin, and united to a flat fan-like bone. In some, as the Salmonidce, the last vertebra is turned upwards. The scales are unusually thin, having flexible plates overlapping each other; some few are furnished with ganoid scales, such as the file-fish, ..