208 KEPTILIA class hi 



Compsemys, Leidy. Known by nearly all parts of the skeleton, with 

 characters as given in the definition of the sub-order. Mesoplastron complete, 

 very much resembling that of Pleurostemum. Hinder lobe of plastron not 

 notched. Upper Jura ; Rocky Mountains. 



[Acknowledgments are due to Drs. S. W. Williston, E. C. Case, and the late G. Baur for 

 assistance in the revision and extension of the foregoing chapter on Chelonia. The published 

 writings of Baur, Boulenger, and Lydekker have also been freely drawn upon.— Editor.] 



Order 7. CROCODILIA. (Hydrosauria, Loricata.) 1 



Lizard-like reptiles, usually of large size, with long, keeled, swimming tail, and 

 entire body covered with horny scales, underneath which along the back and abdomen 

 are usually rows of dermal plates. Investing bones of temporal region contracting 

 into an upper and a lower arcade; quadrate immovably attached to the skull; 

 secondary bony palate developed; parietal foramen wanting ; teeth deeply socketed, 

 confined to margin of jaws. Vertebrae amphiplatyan or procoelous, and among the 

 earlier forms amphicoelous. Cervicals with short, double-headed ribs attached to 

 a ntra ; dorsal ribs long, double-headed, attached to transverse processes. Sternum 

 ossified ; abdominal ribs present. Sacrum composed of two vertebrae. Two pairs of 

 I inihs adapted for swimming and for habitual support of the body. 



Crocodiles possess the highest internal organisation known amongst 

 reptiles. Their general form resembles that of lizards and Rhyncho- 

 cephalians, but their skeletal structure is radically different ; while, on the 

 other hand, there is a fundamental resemblance between their respiratory 

 organs and those of birds. True Crocodilians are apparently initiated in the 

 Lias, and their subsequent evolution is clearly traceable, but their predecessors 

 in the Trias (Parasuchia) are with difficulty distinguished from Rhyncho- 

 cephalians and Dinosaurs. 



Sub-Order 1. PARASUCHIA. Huxley.- 



l'remaxillae greatly elongated. External nares separate and placed far backward, 

 in proximity to the small, upwardly directed orbits ; internal nares occupying their 



1 Literature : 



Brilhl, C. B., Das Skelet der Krokodilien. Vienna, 1862. — Dollo, L., Premiere note sur les 

 Crocodiliens de Bernissart (Bull. Mus. Koy. d'Hist. Nat. Belg. vol. II. p. 309), 1883.— Gray, J. E., 

 Synopsis of the species of recent Crocodilians (Trans. Zool. Soc. vol. VI.), 1862. — Huxley, T. H. 

 Notes on the specific and generic characters of recent Crocodilia (Proc. Linn. Soc. vol. IV. pt. 1), 

 1860. — Koken, E., Die Dinosaurier, Crocodilien und Sauropterygier des norddeutschen Wealden 

 i Palaeont. Abhandl. Dames und Kayser, vol. III.), 1887. — Die Reptilien der norddeutschen unteren 

 Kreide (Zeitschr. deutsch. geol. Ges. vol. XXXV. p. 792), 1883.— Owen, R., Monograph of the fossil 

 Eteptilia of the London Clay (Palaeontogr. Soc), 1849-58.— Monograph of the fossil Reptilia of the 

 Wealden and Purbeck Formations (ibid.), 1853-64. — On the association of dwarf Crocodiles with the 

 diminutive Mammals of the Purbeck Shales (Quar. Journ. Geol. Soc. vol. XXXV. p. 148), 1879.— 

 /'"/■/< /. W. A'., On the structure and development of the skull in the Crocodilia (Trans. Zool. Soc. 

 vol. XL , 1883. — Woodward, A. S., On the literature and nomenclature of British fossil Crocodilia 

 Geol. Mag. [3], vol. II. p. 496), 1885.— The history of fossil Crocodiles (Proc. Geol. Assoc, vol. 

 IX., 1886. 



2 Literature : 



i . E. J)., On the Reptilia of the Triassic Formations of the Atlantic Region of the United 



Proc. Amer. Phil. Soc. vol. XL p. 444), 1871.— Ibid. vol. XVIII. (1878), p. 213.— Huxley, 



'/'. II.. On Stagonolepis robertsoui. and on the evolution of the Crocodilia (Quar. Journ. Geol. Soc. 



vol. XXXI. ],. 423), 1875.— Marsh, 0. C, On Belodon, etc. (Amer. Journ. Sci. [3], vol. L. p. 487), 



1895.— Meijcr, 1L von, Ueber Belodon, etc. (Palaeontogr. vol. X. p. 227), 1863. 



