EXPLANATION OF PLATE 3. L 



Note. — The fish-teeth have not been reversed in drawing, so that the left sides appear to the right, and vice-versa. 



I CHOMATODUS TRUXCATUS. Front view, natural size of average tooth ; from the carboniferous limestone 



of Armagh. 



1 a Profile, ditto. 



2 PETALODOS SAGITTATUS. Front view of old, much worn tooth, natural size, shewing the very long root, 



the tnmcation of the apex by wear, and the unusual puncturing of the surface from the same cause. 



3 View of the inner side of a less worn specimen, shewing that the transverse folds at the base of crown are 



more numerous and much lower in positon on the inner than on the outer part of the root broken off. 



3 a Front view of same tooth. 



3 b Profile of the same tooth. 



3 c Ditto, part of cutting edge, magnified. 



4 PETALODUS PSITTACINUS. Front view of average tooth, natural size, with the large bony roots, slightly 



imperfect at base ; from the carboniferous limestone of Armagh. 



5 PCECILODFS OBLIQUUS. Left posterior tooth, natural size ; from the carboniferous limestone of Armagh. 



5 a Portion of surface, magnified. 



6 PCECILODUS PARALLELUS. Front view of penultimate tooth, natural size. 



6 a Profile of ditto, shewing the spiral inrolment of the crown for the armature of the exterior of the jaw ; from the 



carboniferous limestone of Armagh. 



7 PCECILODUS SUBLiEYIS. Anterior right tooth, natural size; from the carboniferous limestone of Armagh. 



The upper end, when perfect, is a little longer and narrower. 



7 a Profile of ditto, partially she>ving the inrolment of the outer margin ; apex imperfect. 



8 Same tooth imperfect of left side. 



8 a Foreshortened end view of last specimen. 



9 Posterior terminal tooth, left side. 



10 PETALODUS L^VISSIMUS. Natural size of average tooth, outer face; from the carboniferous limestone of 

 Armagh. 



10 a Portion of crown from cutting edge to the transverse folds, magnified. 



II Sketch of four teeth in situ (from Capt. Jones's collecrion), natural size. 



11 a Profile of same specimen. 



12 HELODLTS PLANUS. Narrow oblong specimen, natural size ; from the carboniferous limestone of Armagh. 



12 a Profile of same specimen. 



13 Shorter oblong specimen. 



14 Irregular subrhombic, worn, punctured specimen. 



1 5 Subclavate specimen. 



16 HELODUS MAMMILLARIS. Natural size ; carboniferous limestone of Armagh. 



16 a Profile of ditto. 



17 HELODUS LJEVISSIMUS. Group of four teeth t» situ (in Capt. Jones's collection), natural size; from the 



carboniferous limestone of Armagh. 

 ] 7 a Profile of ditto. 



18 HELODUS DIDYMUS. Obscurely notched, punctured specimen, natural size; carboniferous limestone of 



Armagh. 



18 o .^— Profile of ditto, shewing the posterior margin at a much higher level than the anterior one. 



19 — — Deeply cleft specimen, front view. 



20 Very narrow pointed specimen, back view. 



20 a Ditto, front view. 



