ZOOLOGY. 623 



of the order are represented — the Sphargidids ; tlie Cheloniids, or true 

 sea-turtles; the extinct Propleurids, turtles to some extent intermediate 

 between the sea and snapping turtles; the Chelydrids, or snappers; the 

 Trionychids, or soft turtles ; the extinct Baiinids ; the Emydids, now 

 so abundant in species ; and the Testitudinids, or land tortoises. 



The Dinosaurians. 



Most interesting are the extinct reptiles named Dinosaurians, for 

 various reasons. Many of them were of gigantic size, in certain re- 

 spects they exhibited a considerable degree of specialization, they were 

 also manifested under a variety of modifications, and they either repre- 

 sented the general stock from which the birds originated or were but 

 little removed from that stock. In other words, could we trace the 

 line of the birds backward to their primitive ancestors the naturalist 

 would recognize in the ancestral form a member of the class of reptiles, 

 and in that class he would refer it either to the group of Dinosau- 

 rians, or, as is more likely, to a peculiar earlier one, from which may 

 have originated both types. The richness of the Dinosaurian group in 

 species, in genera, and in families, as well as still more comprehensive 

 groups, had been gradually revealed by different palseontologists, and 

 at length in accelerated ratio, till now Professor Marsh has brought into 

 prominence the variety in structure manifested in a new arrangement of 

 the group. He even considers that the Dinosaurians constitute a di- 

 vision of reptiles of superordinal importance, and calls it a " subclass"; 

 the group is divided into five primary sections, and those are denomi- 

 nated ''orders." The characters given to the several subdivisions, 

 "orders," and "families" are herein condensed from Professor Marsh's 

 diagnoses and contrasted with each other. Whether the groups are of 

 the value claimed by Professor Marsh may be an open question, and the 

 herpetologist must judge for himself what value he would assign to the 

 modifications employed in the diagnoses. 



I. Sauropoda. Dinosaurians with plantigrade (ungulate) feet, front 

 and hind pentadactyle ; fore and hind limbs nearly equal, and without 

 a postpubis ; Atlantosauridce and Morosauridcc. 



II. Stegosauria. Dinosaurians with plantigrade (ungulate) feet, 

 fore and hind pentadactyle ; fore limbs very small and locomotion mainly 

 effected by hind ones ; and with a postpubis ; Stegosauridce, SceUdosau- 

 ridce. 



III. Ornithopoda. Dinosaurians with digitigrade feet, the fore pen- 

 tadactyle, the hind tridactyle, fore limbs small, " limb bones hollow," 

 and with a postpubis ; Goinptonotidce, Iguanodontidce, and Radrosmiridce. 



lY. Theropoda. Dinosaurians with digitigrade (unguiculate) feet, 

 the fore pentadactyle, the hind variable (pentadactyle, tetradactyle, or 

 tridactyle), the " fore limbs very small, limb-bones hollow," and jiost- 

 pubis (?). Megalosauridce, Zanclodontidce, AmpJiisauridce, Labrosauridce. 



V. CcELURiA. (IsTot characterized.) Cceluridce. 



