202 
SELACHII. 
There is yet no evidence of any fusion of the teeth in advance 
of the great posterior plate ; and the narrow specimen described by 
J. IV. Davis 1 as the “ anterior tooth ” of Poecilodus jonesii is the 
foremost of the two dental plates of Deltoclus sidAcevis, being thus 
homologous with the anterior ridge upon the single dental plate of 
Poecilodus. 
As remarked below (p. 212), St. John and IVorthen regard the 
dental plates, assigned in England to the lower jaw of Delto- 
ptijchius , as truly the lower dental plates of Poecilodus. It seems, 
however, much more probable that the dentition of each jaw of 
Poecilodus was transversely ribbed, and this provisional interpreta¬ 
tion is here adopted. Of each of the well-marked British and Irish 
species there are two forms of dental plates—one with the ridges from 
the outer to the inner margin rounded, the other with these ridges 
angulated. The former most probably pertain to the one jaw, the 
latter to the opposite. 
Poecilodus jonesii (M‘Coy). 
1843. Poecilodus jonesii, P. obliquus , and P. transversus, L. Agassiz, 
Poiss. Foss. vol. iii. p. 174 (names only). 
1843. Poecilodus jonesii , J. E. Portlock, Rep. Geol. Londonderry, 
p. 468, pi. xiv. a. fig. 6 (name and fig. only). 
1843. Poecilodus transversus, J. E. Portlock, op. cit. p. 468, pi. xiv. a. 
fig. 7 (name and fig. only). 
1865. Poecilodus jonesii, F. M'Coy, Brit. Pakeoz. Foss. p. 639. 
1855. Poecilodus obliquus, F. M‘Coy, op. cit. p. 640, pi. 3i. fig. 5. 
1883. Poecilodus jonesii, J. W. Davis, Trans. Hoy. Dublin Soc. [2] vol i. 
p. 442, pi. liii. figs. 20, 21, 23 ( non fig. 22). 
1883. Poecilodus obliquus, J. W. Davis, tom. cit. p. 443, pi. liii. fig. 24. 
1883. Poecilodus corrugatus, J. IV. Davis, tom. cit. p. 444, pi. liii. 
fig. 25. 
1884. Poecilodus corrugatus, J. W. Davis, Quart. Journ. Geol. Soc. 
vol. xl. p. 625, pi. xxvii. fig. 21. 
1886. Poecilodus jonesii, J. W. Davis, Geol. Mag. [3] vol. iii. p. 152. 
Type. Detached dental plates. 
Dental plate much elongated antero-posteriorly; coronal cor¬ 
rugations numerous, continuous, and prominent in unworn speci¬ 
mens ; diverging ridges comparatively low ; inner margin slightly 
sinuous. 
Form, df Loc. Lower Carboniferous Limestone: Armagh, Ire¬ 
land ; Ayrshire, Scotland. Upper Carboniferous Limestone: Nor¬ 
thumberland, Yorkshire, and Derbyshire. 
1 Trans. Roy. Dublin Soc. [2] vol. i. (1883), p. 442, pi. liii. fig- 22. 
