CHAPTER VIII. 



DESCRIPTION OF INDIVIDUAL GENERA. 

 PISCES. 



A review of the list of fishes (see table, page 96) shows that by far the 

 larger number were inhabitants of fresh or brackish waters. Indeed, it is 

 doubtful whether there were any which were truly marine. Of the sharks 

 we know little, but it is a well-established fact that some of the living forms 

 of this group are inhabitants of fresh waters, and DoUo has asserted that the 

 form of the caudal fin and the archipterygium form of the lateral fins in 

 Pleuracanthus indicate a fresh-water habitat and are benthal in character.^ 



Pleuracanthus. — Carnivorous, benthal, and fresh-water.'' Size, form, and 

 proportions tmknown. 



Diacranodus, Ctenacanthus, and Anodontacanthus {and possibly Hybo- 

 dus). — These were all carnivorous forms, and probably of the same general 

 habits as Pleuracanthus. Known only from spines and fragments. 



Janassa. — This was evidently a mollusc eater, and from its broad and 

 ray-like form probably kept close to the bottom in shallow water." Known 

 only from the teeth in America. 



The Dipnoans and Crossopterygian and Actinopterygian ganoids were 

 all dwellers in fresh and brackish waters. So little is known of these forms 

 in the Texas fatma that it would be useless to attempt to describe any of 

 them, but it is important to note that not one is indicative of the presence 

 of salt water. Their remains always occiir in sandstones and clays or shales 

 associated with amphibian and reptilian bones, and never, so far as I have 

 observed, with marine invertebrates. This all goes to confirm the supposi- 

 tion that the Texas deposits, other than some of the limestones, were laid 

 down in pools upon the surface of a delta or fiat beyond the reach of marine 

 waters. 



AMPHIBIA. 



The following descriptions and restorations include only the better-known 

 genera: 



Diplocaulus (fig. 13). — ^A great deal of work has been done upon the genus 

 and descriptions of the skull, vertebral columns, and parts of the limbs have 



• Among living fresh- water Selachians are the following: Carcharias gangeticus is found high up in the 

 rivers of India, and also in the Tigris River near Bagdad, 300 miles from the Persian Gulf. The same shark 

 is found in a lake on Viti Levu (Fiji Islands) , which is shut off from the sea by a cataract. Carcharckinus 

 nicaraguensis is found in Lake Nicaragua and its outlet, the Rio San Juan. This shark is confined, so far 

 as known, to fresh waters, and is the only strictly fresh-water shark recorded. 



^ Dollo, Bull, de la Soc. Beige de Geol. de Pal. et d'Hydrol, Tom. xxi, 1906. 



° Jaekel, Geol. Gesell. Zeitsch., 1899; Zittel (Broili), Grundz. d. Paleon., sec. ed., p. 62, figs. 107-109. 

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