ORDER VII 



CROCODILIA 



217 



scutes also overlapping. Wealden ; Belgium. B. 



lapping scutes ; ventral 

 fagesi, Dollo. 



Machimosaurus, v. Meyer (Fig. 318). Imperfectly known. 

 Teeth obtusely conical, strongly striated. Upper Jura. 



Nannosuchus, Owen. Dwarf crocodiles similar to Gonio- 

 pholis, but with slender, curved, smooth, and more uniform 

 teeth. Skull about 10 cm. long. Purbeckian ; Dorsetshire. 



Theriosuchus, Owen. Total length less than 0*5 m. 

 General form approaching that of modern crocodiles. 

 Supratemporal vacuities smaller than the orbits ; teeth 

 tumid and very irregular : mandibular symphysis short. 

 Dorsal scutes overlapping and also united at their outer 

 angles by peg -and -socket articulations ; ventral scutes 



polygonal, united by sutures only, 

 shire. T. pusillus, Owen. 



Purbeckian ; Dorset- 



FlG. 31S. 



Machimosaurus hugi, 

 v. Meyer. Kimmerid- 

 gia ii : Lind nerberg, 

 near Hanover. ' |. 



Sub-Order 4. EUSUCHIA. Huxley. 1 



Snout produced in some forms, but more commonly broad and short. External 

 nostril unpaired and terminal ; internal nasal passage prolonged and floored by the 

 greatly developed secondary palate, formed by plates from the maxillae, palatines, 

 and pterygoids. Eustachian canals completely enclosed; vertebrae mostly procoelous. 

 Other characters as in Mesosuchia. 



This group comprises the later Cretaceous, Tertiary, and modern croco- 

 diles, among which are some long-snouted forms, but the greater number are 

 of the broad-snouted type. As already indicated, they differ from the Jurassic 

 Mesosuchia chiefly in the characters of the palate, eustachian canals, and verte- 

 bral centra, but as to their genetic relations Palaeontology 

 |gj affords no precise information. 



A dorsal armour of bony scutes overlaid by the 

 corneous epidermis is always present among Eusuchid, and 

 frequently also a ventral armour. The dorsal scutes are 

 externally pitted, more rarely radially sculptured, and are 

 often longitudinally keeled. The ventral scutes are 

 flattened, keelless, less prominently sculptured, and some- 

 times divided (Fig. 319). 



The vertebral column comprises about twenty-live pre- 

 sacral vertebrae, two sacrals, and at least thirty-five caudals. 

 Recent crocodiles have all the presacral vertebrae except 

 the atlas and axis procoelous, and the sacrals and anterior 

 caudals amphiplatyan. There are about nine cervicals. The atlas (Fig. 320) 

 is quadripartite, and its unpaired ventral piece (x) has been variously 

 interpreted as the centrum, intercentrum, or hypapophysis. The paired 

 lateral elements are roofed by a median dorsal piece which abuts against the 



1 Literature : 



Ludwig, li.. Fossile Krokodilien aus der Tertiarforuiaticra des MainzerTBeckens (Palaeontogr. 

 Supplem. vol. III.), 1877. — Lydekker, Ii., Siwalik Crocodilia. etc. (Pal. Indica, ser. X. vol. III. 

 p. 209), 1886. — yaillant, L., Etudes zoologiques sur les Crocodiliens fossiles du tertiares (Ann. Soc. 

 Geol. vol. III.), 1872. — Win>,l,ni,r7, A. S.. On the literature and nomenclature of British fossil 

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

 Assoc, vol. IX.), 1886. 



Fig. 319. 



Divided ventral scute 

 of Diplocynodon, sp. Oli- 

 gocene ^Europe. 



