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chalk recall more forcibly the general character of the tertiary fishes 

 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 Placo'idians 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 Balistse, 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 

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

 find fishes 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 below 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 are preserved, 

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

 pey, the chalk, and the oolite series, the capsule of the bulb of the 

 eye is still uninjured; and in many species from Monte Bolca, Solen- 

 hofen, and the lias, we see distinctly all the little blades which 

 form the branchiae. 



It is in the series of deposits below the lias that we begin to find 

 the largest of those enormous sauroid fish whose osteology recalls, 

 in many respects, the skeletons of saurians, both by the closer su- 

 tures of the bones of the skull, their large conical teeth, striated 

 longitudinally, and the manner in which the spinous processes are 

 articulated with the body of the vertebrae and the ribs at the ex- 

 tremity of the spinous processes. 



The small number offish yet known in the transition formations 



K 2 



