220 REPTILIA. 



the Lower Oolites, the latter ranging from the Upper Lias 

 upwards to the Kimmeridge Clay. They are noteworthy for 

 the very small size of the fore limbs compared with the hinder 

 pair a disproportion still more marked in the next genus. 



Metriorhynchus. An Upper Jurassic genus, known by nearly com- 

 plete skeletons from the Oxford Clay of Peterborough, and by various 

 remains from other parts of England, France, and Germany The skull 

 has an elongated tapering form, and is feebly sculptured. The pre- 

 maxillse are scarcely expanded, and the nasals do not reach them; the 

 external narial opening and the supratemporal vacuities are very large; 

 and the orbits are directed chiefly laterally, while the prefrontal bones 

 are unusually large and form an overhanging ledge. The teeth are slender 

 and carinated, at least 20 in number in each half of the jaw above and 

 below. Sclerotic plates occur in the eye. No trace of dermal armour has 

 been met with. 



Dakosaurus, also an Upper Jurassic genus, has the skull comparatively 

 short and broad, with the nasals reaching the premaxillee and the external 

 narial opening. The teeth are relatively larger and fewer than those of 

 the genera mentioned above, not exceeding 20 in number on each side 

 of either jaw ; they are oval in section, smooth, and with two opposite 

 keels. There is no vacuity in the side of the mandibular ramus. The 

 remainder of the skeleton is very imperfectly known. The external 

 head-bones are smooth or only feebly sculptured, and no dermal scutes 

 have been observed. The typical species, D. maximus, was founded on 

 fragments from the Corallian and Lower Kimmeridgian of Wiirtemberg 

 and Bavaria. Fine skulls are known from the English Kimmeridge 

 Clay. 



Theriosuchus. This is a dwarf crocodile, only about 0*45 m. in 

 length, and the earliest type closely approaching the modern crocodiles 

 and alligators in outward form. The facial portion of the skull, in 

 advance of the orbits, constitutes only about one-third of its entire 

 length, thus retaining in the adult condition somewhat analogous pro- 

 portions to those observed temporarily in the young of living Crocodilia ; 

 and the nasal bones overhang the aperture of the external nostril, which 

 seems to have been terminal. The supratemporal vacuities are smaller 

 than the orbits ; and the opening of the posterior nares on the palate is 

 definitely proved not to have been displaced backwards by secondary 

 outgrowths from the pterygoid bones. The teeth are tumid, and more 

 varied both in size and shape than those in any other known member 

 of the order. The mandibular symphysis is short. The body is pro- 

 tected, both dorsally and ventrally, by pitted scutes, the upper shield 

 consisting of only two longitudinal rows, and the lower of more irregular 

 rows. The dorsal scutes are rectangular, not only overlapping but also 

 united at their outer angles by a " peg-and-socket " articulation such as 



