202 
sELAcnir. 
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. W. Davis ‘ as the “ anterior tooth ” of Poecihdvs jonmi is the 
foremost of the two dental plates of Deltodus mhhevis, being thus 
homologous with the anterior ridge upon the single dental plate of 
Poecilodns. 
As remarked below (p. 212), St. John and Worthen regard the 
dental plates, assigned in England to the lower jaw of Delto- 
iHi/chitis, as truly the lower dental plates of Pcecilodm. It seems, 
liowevor, much more probable that the dentition of each jaw of 
Piedlodus was transversely ribbed, and this provisional interpreta- 
tion is hero 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). 
184.3. Poecilodus jonesii, P. ohliquus, and P. tmnsversus, Ij. Agassiz, 
Poiss. Foss. vol. iii. p. 174 (names only). 
1843. Poecilodus jonesii, J. E. Poi'tlock, Rep. Qeol. Ijondonderry, 
p. 468, pi. xiv. «. fig. 0 (name and fig. only). 
1843. Pojecilodus tramversus, .1. E. Portlock, o/i. cit. p. 408, pi. xiv. «. 
fig. 7 (name and fig. only). 
1856. Pcecilodm jonesii, F. M‘Coy, Brit. Palieoz. Foss. p. 630. 
185.6. Pcecilodm ohltcjuus, F. IM'Coy, op. cit. p. 040, pi. 3i. fig. 5. 
1883. Poecilodus jonesii, J. W. Davis, Trans. Roy. Dublin Soc. [2] vol i. 
p. 442, pi. liii. fig.s. 20, 21, 23 (non fig. 22). 
1883. Pcecilodm obliquus, J. W. Davis, tom. cit. p. 443, pi. liii. fig. 24. 
1883. Pcecilodm corruc/citus, .1. W. Davis, tom. cit. p. 444, pi. liii. 
fig. 26. 
1884. Pcecilodm corruyatns, J. W. Davis, Quart. Journ. Geol. Soc. 
vol. xl. p. 625, pi. xxvii. fig. 21. 
1880. Pcecilodm jonesii, J. W. Davis, Qeol. Mag. [3] vol. iii. p. 152. 
Type. Detached dental plates. 
Dental plate much elongated antero-postoriorly ; coronal cor- 
nigations numerous, continuous, and prominent in unworn speci- 
mens ; diverging ridges comparatively low ; inner margin slightly 
sinuous. 
Form. ^ Loc. Lower Carboniferous Limestone: Armagh, Ire- 
land ; Ayrshire, Scotland. Upper Carboniferous Limestone : Nor- 
thumberland, Yorkshire, and Derbyshire. 
‘ Trans. Eoy. Dublin Soc. [2] vol. i. (1883), p. 442, pi. liii. fig- 22. 
