Geological Distribution of Fossil Fish. 4-61 



sillers perfectly identical with those of our seas, except the little fish 

 which is found in Greenland in geodes of clay, and whose geologi- 

 cal age is unknown to him. 



The species of the crag of Norfolk, the superior subapennine for- 

 mation, and the molasse, are related for the most part to genera 

 now common in tropical seas ; such are the Platax, the large Car- 

 charias, the Myliobates, with large palatal plates, and others. In 

 the inferior tertiary formations, the London clay, the calcaire gros- 

 sier of Paris, and Monte Bolca, a third at least of the species belong 

 to genera which exist no longer. The chalk has more than two 

 thirds of its species referrible to genera which have now entirely dis- 

 appeared. In it we already even see some of those singular forms 

 which prevail in the Jurassic series. But as a whole the fish of the 

 chalk recall more forcibly the general character of the tertiary fish 

 than that of the species of the Jurassic series. 



If we paid attention only to fossil fish in the grouping of geolo- 

 gical formations on a large scale, the author thinks it would be more 

 natural to associate the cretaceous with the tertiary strata than to 

 place the former among the secondary groups. Below the chalk 

 there is not a single genus which contains recent species, and even 

 those of the chalk which have them contain a much greater propor- 

 tion of species which are only known as fossil. The oolitic series, 

 to the lias inclusive, forms a very natural and well defined-group, 

 in which also must be included the Wealden, in which Mr. Agassiz 

 states he has not found a single species referrible even to the genera 

 of the chalk. Henceforth, the two orders which prevail in the pre- 

 sent creation are found no more; whilst those which are in a small 

 minority in our days, appear suddenly in great numbers. Of the 

 Ganoidians, those genera which have a symmetrical caudal fin are 

 found here, and among the Placoidians those above all predominate 

 which have their teeth furrowed on both the external and internal 

 surface, and have large thorny rays. For it is now certain that 

 those great rays which have been called Ichthyodorulites, belong 

 neither to Silures nor Balistas, but are the rays of the dorsal fin of 

 the great Squaloids, whose teeth are found in the same strata. 



On leaving the lias to come to the inferior formations, we observe 

 a great difference in the form of the posterior extremity of the body 

 in the Ganoidians. All have their vertebral column prolonged at 

 its extremity into a single lobe, which reaches to the end of the 

 caudal fin, and this peculiarity extends even to the most ancient 

 fish. Another observation worthy of attention is, that we do not 

 find fish decidedly carnivorous before the carboniferous series; that 

 is to say, fish provided with large conical and pointed teeth. The 

 other fish of the secondary series before the chalk appear to have 

 been omnivorous, their teeth being either rounded, or in obtuse 

 cones, or like a brush. 



The discovery of coprolites containing very perfect scales offish 

 which had been eaten, permits us to recognise the organized beings 

 which formed the food of many ancient fish ; even the intestines, 

 and in some fossil fish of the chalk the whole stomach is preserved, 

 with its different membranes. In a great number offish from Shep- 



