112 PISCES 



CLASS I 



the corresponding strata of Werther, near Halle, the Departments of Calvados, 

 Yonne, and Cöte-d'Or in France, and of Ilminster and Whitby in England, 

 again yield a considerable number of species. The Selachians persist in 

 undiminished numbers. Undina gulo, Egerton, from Lyme Regis represents the 

 Coelacanthidae, Chondrosteus the cartilaginous ganoids. The majority of the 

 Liassic fishes, however, belong to the scaly Ganoids of the order Lepidostei, 

 though a few genera of the heterocercal Palaeoniscidae still survive. A new 

 element in the Liassic fish fauna is formed by the thin-scaled Amioids, in 

 which the vertebral column is still bent upwards to the upper lobe of the tail, 

 and remains incompletely ossified. A single species from the Lower Lias of 

 England (Mesodon liassicus, Eg.) indicates the first appearance of the 

 Pycnodontidae. Among bony fishes a few small Clupeoids (Leptolepis) may 

 be mentioned. Ceratodus and Pholidophorus are present in the Lower Jura of 

 the Western United States. 



In the Middle Jura shaly deposits with well-preserved fish skeletons are 

 wanting. Our knowledge of the fish fauna of the period is thus confined 

 to detached teeth, fin spines, bones, and scales, which occur occasionally. 

 Almost all the genera observed in the Dogger occur in addition in the Lias 

 or the Upper Jurassic. Of the latter the most numerous discoveries have 

 been made in the fissile limestones of the neighbourhood of Solenhofen, 

 Kelheim, and Eichstädt in Bavaria, Nusplingen in Würtemberg, and Cerin in 

 the Department of Ain, France, An abundance of beautifully preserved 

 skeletons of Selachians, Ganoids, and Teleosteans have been obtained from 

 these localities, to which must be added the Portlandian Limestone of Soleure, 

 Neuchätel, Hanover, and Boulogne-sur-Mer, and the Purbeck Beds of England 

 as formations yielding well-preserved jaw- bones, teeth, spines, scales, and 

 vertebrae. The heterocercal Palaeoniscids have become reduced to a single 

 genus (Coccolepis). Of sharks and rays, complete or partially well-preserved 

 skeletons are known, which indicate close relationships or absolute identity 

 with various still surviving genera. The Cestraciontidae and Lamnidae are 

 also represented by several extinct genera, and the Holocephali are much 

 more numerous than in the Lias. Among the Ganoids the Coelacanthidae 

 attain their maximum development in varied forms. The large majority of 

 the Upper Jurassic fishes consist of Lepidostei and Amioidei, with Teleostei of 

 the family Leptolepidae. 



With the beginning of the Cretaceous system there is an important change 

 in the fish fauna, so that the previously dominant Ganoids become more and 

 more displaced by Teleosteans. This Substitution is almost complete in the 

 middle and upper divisions of the Chalk ; in the Lower Cretaceous, on the 

 other band, there are still a few types of Ganoids surviving from Jurassic 

 times. The fish fauna of the Cretaceous system thus falls into two well- 

 marked sections, to the lower of which belong the light-coloured fissile lime- 

 stones of Pietraroza, the limestones of Castellamare, and Torre d'Orlando near 

 Naples, of Comen (Istria), Crespano (Vicentin), Lesina (Dalmatia), and Grodischt 

 in the Carpathians, and the Neocomian deposits of the Yoirons, near Geneva. 

 The normal deposits of the Middle and Upper Chalk chiefly contain teeth, 

 vertebrae, and isolated fragments of Selachians, Chimaeroids, Pycnodonts, and 

 Physostomes ; the fissile limestones of the Lebanon, the marly sandstone of 

 Westphalia, and the Niobrara Chalk of Kansas, on the other band, yield a con- 

 siderable number of well-preserved skeletons. Among these the Ganoids are 



