Vol. 60.] EDESTUS IX THE COAL-MEASURES OF BRITAIN. 7 



end of the older one, and that this by growth gradually ensheathed 

 the one above. This seems most likely to be the correct interpre- 

 tation, although doubt has been thrown upon the supposed non- 

 grooved segment, which was thought to be the first formed. 



That the curved and toothed ichthyodorulites, to which the name 

 of Edestus is properly restricted, belonged to a fish closely allied to 

 that which carried the ' spiral saw,' Helicoprion, is generally 

 agreed, but it is by no means proved that the two forms had a 

 similar function. 



Dr. Eastman has shown good reason for thinking that the 

 enrolling of the symphysial teeth of Campodus is an indication of 

 the nature of the spiral of Helicoprion, although he was not the 

 first to suggest this interpretation. There is, however, but a 

 distant relationship between these two genera, even if his idea that 

 they are both Cestracionts should prove correct. That Carapylo- 

 prion is nearly related to Helicoprion will be readily admitted ; 

 indeed, there seems no obvious reason why the fossils referred to 

 this genus may not have been parts of spirals similar to that of 

 Helicoprion, and if so they might conveniently have remained in 

 that genus. 



With regard to Edestus, the form of each tooth-crown and base 

 is so unlike those in Helicoprion that its generic distinction will 

 not be disputed ; but, at the same time, its near relationship to 

 Helicoprion has not been questioned. 



However anomalous the • spiral saw ' of Helicoprion may be, it 

 seems most in accordance with our present knowledge to regard it 

 as the enrolled dentition at or near the symphysis of an elasmo- 

 branch, possibly allied to Cestracionts. That the forms referred to 

 Edestus are of the same nature seems less probable ; and, while 

 admitting that this interpretation may prove correct for them also, 

 it still seems to me that these straighter forms, with large anteriorly- 

 projecting bases, are more likely to be dorsal defences. 



Bibliographical List. 



1. J. Ward. On Marine Bands in the Coal-Measures of North Staffordshire.] 



Geol. Mag. vol. ii (I860) pp. 234 & 286. 



2. E. Hull & A. H. Geeex. Trans. Maneh. Geol. Soc. vol. iii (1862) p. 348. 



3. E. Hull & J. W. Salter. Mem. Geol. Surv. ' Geolosy of the Country 



around Oldham ' 1864, p. 64. 



4. E. Hitchcock. 'Account of the Discovery of the Eossil Jaw of an Extinct 

 Family of Sharks from the Coal-Formation' Proc. Amer. Assoc. Adv. Sci. 

 (Ninth Meeting, Providence, 1855) Cambr. 1856, p. 229. 



5. Joseph Leidt. ' Indications of Five Species, with Two Xew Genera, of Extinct 

 Fishes ' Proc. Acad. Xat. Sci. Philad. vol. vii, 1854-55 (1856) p. 414. Also Journ. 

 Acad. Nat. Sci. Philad. ser. 2. vol. iii, 1856 (1858) p. 159 & pi. xv. 



6. . ' Remarks on certain Extinct Species of Fishes ' Proc. Acad. Nat. Sci. 



Philad. vol. viii, 1856 (1857) p. 301. 



7. K. Owen-. ' Palaeontology ' 2nd ed. Edinburgh, 8vo (1861) pp. 123-24 & fig. 38. 



8. J. S. Newberry. Geol. Surv. Illinois, vol. ii (1866) p. 84 & pi. iv. 



9. J. S. Newberry & A. H. Worthed. Ibid. vol. iv (1870) p. 350 & pi. i, fig. 2. 



10. H. Trautschold. 'Die Kalkbriiche von Mjatschkowa ' Nouv. Mem. Soc. Imp. 

 Nat. Moscou, vol. xiv (1879) p. 49 & pi. vi, fig. 8. 



11. M. Lohest. ' Recherches sur le«; Poissons des Terrains paleozoiques de Belgique ' 

 Ann. Soc. Geol. Belg. vol. xi (1883) p. 314. 



