984 ZOOLOGY. 
indefinite number of joints, all united into a strong paddle or oar. In this ~ 
respect they 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 vertebre 
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 longitudinal groove, bearing 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. ‘That 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 this family, we have space to mention but 
two, which perhaps offer the extremes of structure. The first of these is 
Ichthyosaurus (pl. T4. 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 cartilagmous fin near the tail. The 
head was very large and pointed, the neck very short, and the tail very 
long; the entire animal having an acutely sub-fusiform shape. Plesiosaurus 
(pl. 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 vertebrz, and the neck 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. Pterosaurvi. Of all anomalous reptilian animals, Pterodacty- 
lus, the single genus composing the family, presents perhaps the most remark- 
able features. Even its position in the class Reptilia 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 connecting 
link between the two last mentioned classes. Wagler went so far as to 
construct 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 which distinguishes the pterodactyle from all other reptiles is to 
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