32 FOSSIL REPTILIA OF THE LONDON CLAY. 



and dental structure on which the characters of the restricted genus Crocodilus of 

 modern Zoology are founded ; but they are associated with a general form of the head 

 which approaches more nearly to the Gavials than does that of the Crocodilus toliapicus, 

 and which are most nearly paralleled amongst the known existing true Crocodiles by 

 the Crocodilus Schlegelii. This Bornean species was, in fact, originally described as a 

 new species of Gavial, but the nasal bones, as in the fossil from Sheppy figured in 

 T. II, 15, extend to the hind border of the external nostril. 



The fine subject of T. Ill, forms part of the collection of J. S. Bowerbank, Esq. 

 F.R.S., which is well known for its rich and varied illustrations of the fossils of the 

 Isle of Sheppy. 



The following are some of its admeasurements : 



Feet. Inches. Lines. 

 Total length from the occipital condyle to the end of the 



preniaxillaries .... 



Breadth across the hinder angles of the supracranial platform 



Do. across the orbits . • . 



Do. of the intertemporal space 



Do. of the interorbital space . 



Do. across the external nostril 

 From the occipital condyle to the orbit 

 From the orbit to the external nostril 



The skull yielding the above dimensions is much smaller than that of the Crocodilus 

 toliapicus, T. II ; but it cannot have belonged to a younger individual of the same 

 species, because, in existing Crocodiles, the part of the skull anterior to the orbits is 

 proportionally shorter in the young than in the old individuals, as may be seen by 

 comparing the figures which Cuvier has given of the skulls of three individuals of 

 different ages of the Crocodilus biporcatus, in figures 4, 18, and 19, of plate 1 of the last 

 volume of the ' Ossemens Fossiles,' 4to, 1824 ; whereas the part of the skull anterior to 

 the orbits is relatively longer and more slender in the smaller fossil skull now described 

 than in the larger one on which the species Croc, toliapicus is founded. We have, 

 therefore, satisfactory proof that two species of true Crocodile existed during the de- 

 position of the Eocene Clay at the actual mouth of the Thames, and have left their 

 remains in that locality. 



Their specific distinction is further illustrated by the different forms and propor- 

 tions of particular parts of the skull. The alveolar border is more nearly straight ; the 

 transverse expansion of the maxillaries (21) is less, whilst that of the preniaxillaries 

 (22) is greater : the interorbital space is broader and more concave. The teeth are 

 more uniform in size, are more regularly spaced, and are wider apart : they are, likewise, 

 upon the whole, larger in proportion to the size of the jaw. Figure 5, T. Ill, shows 

 the crown of a new tooth just emerging from the second socket of the maxillary bone 

 of the natural size ; figure 6 is the fourth tooth of the premaxillaiy, fully formed ; fig. 7 



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