A manual of zoology for the use of students with a general introduction on the principles of zoology

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1871 Excerpt: ...The recent genus Hyalea is represented in the Tertiary period (Miocene). Cephalopoda.--The Cephalopods are largely represented in all the primary groups of stratified rocks from the Lower Silurian up to the present day. Of the two orders of Cephalopoda, the Tetrabranchiata is the oldest, attaining its maximum in the Palaeozoic period, decreasing in the Mesozoic and Kainozoic epochs, and being represented at the present day by the single form Nautilus pompilius. Of the sections of this order, the Nautilida proper and the Orthoceratida are pre-eminently Palaeozoic, and the Ammonitida are not only pre-eminently but are almost exclusively Secondary. Of the abundance of the two former families in the Silurian seas some idea may be obtained when it is mentioned that over a thousand species have been described by M. Barrande from the Silurian basin of Bohemia alone. The Nautilida proper have gradually decreased in numbers from the Palaeozoic through the Secondary and Tertiary periods to the present day. The Orthoceratidat died out much sooner, being exclusively Palaeozoic, with the exception of the genera Orthoceras itself and Cyrtoceras, which survived into the commencement of the Secondary period, finally dying out in the Trias. The second family of the Tetrabranchiata--viz., the Ammonitidee--is almost exclusively Secondary, being very largely represented by numerous species of the genera Ammonites, Y Ccratites, Baculites, Turrilites, &c The only Palaeozoic genera are Goniatites and Bactrites, of which the former is found from the Upper Silurian to the Trias, whilst the latter is a Devo 'Fig. 122.--Shells of Secondary Cephalopoda, i Ancyloceras Matkenmietuus; 2 Snwhites aqualis; 3 Crioceras Duvalit; 4 Hamitts attenuates; 5 Turriiites aitflatus. nian form. Th...