HARDWICKE'S SCIENCE-GOSSIP, 



229 



is represented abundantly in the Eocene strata of 

 Sheppey, Barton, and Bracklesham, and the teeth 

 may always be easily recognised by the delicate 

 longitudinal stria; on the hinder side. L. {Odontaspis) 

 Hopci, of the same stratigraphical position, much 

 resembles the last species, but is distinguished by the 

 absence of stria:, and by the more cylindrical shape 

 of the tooth. Another species from the Eocene is 

 L. compressa, which appears to be almost intermediate 

 between Lamua and Otodns, and is remarkably 

 flattened. 



Otodus is an entirely extinct genus, and ranges from 

 the Lower Cretaceous strata to the Upper Eocene. 

 The teeth are distinguished from those of Lamna by 

 the more compressed character of the crown, and 

 the much less elongated and branched condition of 

 the root ; the lateral denticles, too, which are always 

 present, are large in proportion to the central cone. 



from those of Otodus in possessing no lateral denticles, 

 but are very similar in other respects. The earliest 

 species occur in the Gault, and the genus survives to 

 the present day. O. viacrorhiza (fig. 138), from the 

 Gault and Greensand, is characterised by its very 

 depressed form, and the consequent great breadth of 

 the root. 0. Maiitellii (fig. 136) is a species abundant 

 in the Chalk, and sometimes occurring in the Green- 

 sand, No teeth of this genus appear to have been 

 recorded hitherto from the English Eocene forma- 

 tions, but O. xiphodon and 0. hastalis are character- 

 istic fossils of the Pliocene Crags, and these are also 

 met with in Eocene and Miocene strata on the Con- 

 tinent. 



The only remaining genus of Lamnidce of much 

 pal,Eontological importance, is Carcharodon, of 

 which but one species, C. Rondeletii, survives in our 

 present seas. It first appears in early Eocene times,_ 



Fig. I'i^.^-Oxyrhtna tnacrorkiza. 



Fig. i^i.-^Carcharsdon ang7istidens. 



Fig. 137. — LamnM 

 elegans. 



Fig, 



139. — Upper tooth 

 ot Notidanus. 



Fig. 140. — Notidatius 

 primigenius. 



Fig. 142. — Noti- 

 danus microdon. 



Fig. 143. — N. serra- 

 tissimiis (all figs, 

 nat. size). 



Of the earlier species, O. appendiculatus (fig. 131) is 

 the most important, and occurs in Cretaceous rocks 

 almost wherever they are developed, being found in 

 Britain, many localities on the Continent, and even 

 in the New World. The root of this tooth is very 

 thick and depressed, and both crown and denticles 

 are likewise particularly stout. O. ohliqwis is the 

 largest known species, and is met with in Eocene 

 strata ; in form, the teeth are closely similar to the 

 Carcharodon shown in fig. 141, but there are no traces 

 of serrations on the edges, and the size is occasionally 

 much greater. Some are oblique, as in the figure, 

 and some straight, the former being generally regarded 

 as belonging to the upper jaw, and the latter to the 

 lower. Another Eocene species is O. 7nacrotiis (fig. 

 135), remarkable for the large development of the den- 

 ticles and the compressed form of the tooth, and, like 

 the previously mentioned species, having a wide 

 geographical range. 



The teeth of Oxyrhma (fgs, 136 and 138) differ 



attains its maximum development in the Miocene, 

 and has since been gradually approaching extinction. 

 The teeth are flattened, triangular, with or without 

 lateral denticles at the base of the principal cone, and 

 in all cases serrated on the edges ; although very 

 similar to the teeth of Carcharias in external appear- 

 ance (except as regards size), they are easily distin- 

 guished by being solid throughout, and the dentition' 

 of the lower jaw is much more like that of the upper 

 than in the latter genus. The English Eocene 

 species are C. angiistidens (with which Agassiz' C, 

 lieterodon is now incorporated) and C. subserratits, — 

 the former (fig. 141) with lateral denticles, from the 

 Bracklesham and Barton beds, and the latter, 

 without lateral denticles, from the London Clay of 

 Sheppey. But the most important species of the 

 genus is C. megalodon, a form whose enormous teeth 

 are not unfrequently met with six inches long and 

 nearly five inches across the base, and occur in 

 Miocene (and perhaps later} deposits almost all over 



