322 PALEONTOLOGY 



The examples of the Mammalia first met with in tertiary 



strata are the Coryphodon and Palccocyon, respectively repre- 

 senting the ungulate (herbivorous) and unguiculate (carnivor- 

 ous) modifications of the class ; their remains have been found 

 in the plastic clay and equivalent lignites in England and 

 France. 



Genus Coryphodon, Ow. — Barely has the writer felt more 

 misgiving in regard to a conclusion based, in palaeontology, on 

 a single tooth or bone, than that to which he arrived after a 

 study of the unique fragment of jaw with one tooth dredged 

 up off the Essex coast, and on which he founded the genus 

 Coryphodon.* 



The marked contraction of the part of the jaw near one 

 end of the tooth seemed, at first view, clearly to show it to be 

 the narrower fore part of the ramus ; in that case the tooth 

 would have been a premolar, and of comparatively little value 

 in the determination of a genus or species. But a closer in- 

 spection showed the line of abrasion of the summits of the two 

 transverse ridges of the tooth to be on one side, and the gene- 

 ral law of the relative apposition and reciprocal action of the 

 upper and lower grinders in tapiroid Pachyderms determined 

 that those oblique linear abrasions must be on the hinder 

 side of the ridges. The smaller characters carried conviction 

 against the showing of the larger and more catching ones. So, 

 in determining the position of the nautilus in its pearly abode, 

 when the animal without its shell was first brought to Eng- 

 land in 1831, the reasons afforded by some small and incon- 

 spicuous parts in like manner outweighed the firsl impressions 

 from more obvious appearances, as well as the bias from the 

 general analogies of testaceous Univalves. Some contemporary 

 naturalists asserted, and for a time it was believed, that the 

 nautilus had been put upside down in its shelly just as some 



* History of British Fossil Mammals, 8vo, p. 209, figs. 103. 104. 

 f In plate i. of tlie writer's Memoir of the Nautilus, 4to, 1832. 



