118 
1CHTH Y OD OE.TJL J.'I'ES. 
XI. Slender elongated spines, bilaterally symmetrical, with the 
internal cavity only open at the extremity of the base, and 
little or no smooth inserted portion. 
Genus GNATHACANTHUS, Davis. 
[Trans. Roy. Dublin Soc. [2] vol. i. 1888, p. 363.] 
Spine laterally compressed, with one margin acute, the other flat¬ 
tened ; sides ornamented with longitudinal ridges, smooth or tuber- 
culated; acute margin with a single series of large denticles, flattened 
margin with a double series of smaller denticles. 
The base of the spine is unknown, and Gnathacanihus is thus only 
provisionally placed in this group of Ichthyodorulites. 
Gnathacanthus triangularis, Davis. 
1883. Gnathacanihus triangularis, J. IV. Davis, tom. cit. p. 363, pi. xlviii. 
fig. 11. 
Type. British Museum. 
The type species. 
Form. 6f Log. Lower Carboniferous Limestone : Armagh. 
P. 2891. Type specimen. Enniskillen Coll. 
Gnathacanthus striatus, Davis. 
1883. Gnathacanthus striatus, J. W. Davis, tom. cit. p. 364, pi. xlviii. 
fig. 12. 
_ t 
Type. British Museum. 
Form. § Log. Lower Carboniferous Limestone: Armagh. 
P. 2892. Type specimen. Enniskillen Coll. 
P. 2892 a. Fragment. Enniskillen Coll. 
Genus APATEAGANTHUS, nov. 
Spine elongated, slender, very gradually tapering, extremely com¬ 
pressed laterally ; sides ornamented with irregular series of tuber- 
culations ; posterior border with one (? or two) close series of acute, 
hook-shaped, downwardly-pointing denticles. 
