284 ZOOLOGY. 



indefinite number of joints, all united into a strong paddle or oar. In this 

 respect tliey resemble fishes, an analogy which perhaps detracts from that 

 eminence which the alveolar character of the teeth would imply. The entire 

 framework is eminently calculated for progression in the water, the anterior 

 extremities being more powerful than the posterior. The numerous vertebras 

 have biconcave articulating surfaces, and the bodies are rather broader than 

 long. The immense eyes were provided with a bony sclerotic hoop, as in 

 birds, composed of numerous pieces. This hoop, however, instead of being 

 imbedded in the sclerotic of the eye, was probably attached to the margins of 

 the orbit anterior to the eye. The teeth were large and conical, arranged in 

 a lon'i'itudinul groove, bearinj]' traces of a subdivision into alveoli. The 

 skin was probably naked. The entire structure of the enaliosaurians indicates 

 a highly rapacious character, well fitted to make them the terror of the 

 deep. Tliat their food consisted mainly of fishes is shown by the fact that 

 their coprolites, or fossilized excrement, always contain scales or bones of these 

 animals. 



The enaliosaurians inhabited the seas of Europe during the deposit of the 

 Trias and Jura formations. No species have as yet been detected in North 

 America. 



Of the numerous genera of tliis family, we have space to mention but 

 two, which perhaps offer the extremes of structure. The first of these is 

 IchtJujosnuriis {pi. 74. fig. 83), a form which probably resembled that of 

 some living cetaceans, as the dolphin. Like some of them, too, it was 

 probably furnished with a vertical cartilaginous fin near the tail. The 

 iiead was very large and pointed, the neck very short, and the tail very 

 long ; the entire animal having an acutely sub-fusiform shape. Plesiosaurus 

 (pi. 74, fig. 82) presents conditions of external appearance precisely the 

 reverse of the last genus. With a very small head, the neck was of such 

 enormous length as greatly to exceed, in this respect, any other animal. 

 Some species have as many as 40 cervical vertebrae, and the nock must 

 have had a flexibility and freedom of motion far exceeding that of the swan, 

 or any of the herons. In mammalia, this number never exceeds seven ; 

 birds have from nine to twenty-three ; in living reptiles, from three to eight. 

 The tail of Plesiosaurus was shorter, and the feet weaker and more slender 

 than those of Ichthyosaurus. Some species of both genera exceeded 20 feet 

 in length. 



Fam. 10. Pterosnurii. Of all anomalous reptilian animals, Pterndacty- 

 lifs, the single genus composing the family, presents perhaps the most remark- 

 able features. Even its position in the class ReptUia has been allowed, 

 comparatively speaking, but recently, some writers assigning it to fishes, 

 some to mammalia, others to birds ; while a few saw in it a c mnecting 

 link between the two last mentioned classes. Wagler went so far as to 

 constiuct for it a new class of vertebrate animals, in which he likewise 

 placed the enaliosaurians and the monotrematous mammalia. In appearance 

 they must have somewhat resembled, when living, enormous bats ; and 

 would have well illustrated the fabulous dragon of olden times. The pecu- 

 liarity Avhich distinguishes the pterodactyle from all other reptiles is to 

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