OXYRHINA. 205 



SiH'clfi.e Gharacters.—A very small species, the crown of the anterior teeth only 

 attaining a height of about 1"2 cm. Dental crown always very narrow and deep, 

 extending along the wider root at its base ; the divergent branches of the root 

 considerably elongated in the teeth near the symphysis. 



Description of Specimen.'^. — Tliis species is known only by detached teeth, of 

 which a selection from the English Chalk is shown in PL XLIII, figs. 16 — 20. Even 

 in the symphysial teeth (figs. 1(3, 17) the crown widens at its base into a short 

 extension along the root both in front and behind. The crown in these teeth has 

 a very slight sigmoidal bend, while the root exhibits a cleft for the nutritive 

 foramen on its inner face (fig. 16). In the lateral and hinder teeth (figs. 18 — 20) 

 the crown is still remarkably narrow and very little inclined, but the inner face of 

 the root does not appear to be marked by a cleft. The crown is always extremely 

 smooth, with thin, sharp edges. 



Horizons and Localities. — Zone of TcrcbnUidina gracilis : Whyteleafe, Surrey 

 (G. E. Dibley). Zone of Ilolaster subglohosns : Burham and Hailing, Kent; 

 Griynde, Sussex; Oxted and Guildford, Surrey; Cherry Hinton, Cambridgeshire. 

 Zone of SchloenhacMa varians : Dover, Kent. Also Upper Greensand and 

 Cambridge Greensand. 



3. Oxyrhina crassidens, Dixon. Plate XLIV, figs. 1, 2. 



1843. Oxyrhina manteUi, L. Agassiz {errore), Poiss. Foss., vol. iii, pi. xxxiii, fig. (i. 



1850. Oxyrhina crassidens, F. Dixou, Greol. Sussex, p. 367, pi. xxxi, fig. 18. 



1889. O.ryrhini crassidens, A. S. Woodward, Catal. Foss. Fishes B. M., pt. i, p. 382. 



Ti/2)e. — Nearly complete tooth from a Turonian zone ; British Museum. 



Specific Characters. — Teeth extremely robust, of large size, the crown attaining 

 a height of about -1 cm. Dental crown narrow and deep, extending at its base 

 along the wider root, where its edge is usually coarsely crimped; outer coronal 

 face irregularly convex, with few vortical wrinkles; inner face extremely convex 

 and smooth, but with fine, short basal wrinkles. Root of tooth with a considerable 

 inward prominence immediately below the base of the crown, and only a faint 

 shallow groove for the nutritive foramen. 



Descrijjtioii of Specimens. — The type tooth in the Dixon Collection (PL XLIV, 

 fig. 1) is noteworthy for the excessive crimping of its lateral basal extension on the 

 side best preserved, and its inner face shows clearly the fine vertical wrinkles at 

 the lower border of the crown (fig. la). A more elevated and less robust tooth 

 (PL XLIV, fig. 2), evidently from a more anterior position in the jaw, has a less 

 crimped lateral basal extension, but its inner face (fig. 2 a.) is similarly wrinkled 

 at the base. More than half of its root is well preserved, showing the character- 

 istic inward prominence and the faint shallow groove on the middle of its inner 



