109 



'i hi \ |i..rti"ii .-I' th, .1, utal (' ivi OB nt "i tlic II|>|MT uu d .1 / '/' - 



There re two row* of mull denticle* on both ikies in this specimen. The difference of 

 thickness in the anterior worn denticle*, and the posterior Uter developed one* intruded to 

 replace them, is worthy of notice. The bate* of the denticle* *how the fissure* by wliirh thr 

 vessels and nenre* penetrate the medullarj cavities and canal* of the dental tubstance. 



547. A portion of the dental pavement of a lower jaw of a Xygobalr*. The series 

 next the middle one, on the left side, is divided into two, which renders the 

 pavement unsymmctrical, an anomaly without doubt accidental and peculiar 

 to the individual from which the specimen was derived. //////AT///// 



548. A portion of the lower jaw and dental (wvement of the same species of / 



batf. The abnormal division is not present in either of the lateral series of 

 denticles, and their arrangement is symmetrical. limit- nan. 



549. The right moiety of a small, dried, bisected specimen of an Eagle Ray 



bates), showing the disposition of the massive crushing dental plates of the 

 palato-maxillary and mamlibulur arches. 



The palato-maxillary series is distinguished by it* greater degree of curvature : it is placed 

 vertically with the convex grinding surface turned backwards and downwards, the lower and 

 anterior border working upon the almost horizontal surface of the mamlibular pavement . 



Hunterian. 



550. A part of the dental pavement of the upper jaw of an dSfo6afe. The grinding 



surface is convex antero-posteriorly, and sinuous transversely, being slightly 

 concave in that direction at the sides. //un(ehan. 



551. Part of the dental pavement of the upper jaw of a very large 



Brit. 



552. A portion of the upper jaw, with the dental pavement, of an jEtobatr*. This 

 subgenus is characterized by the single series of teeth, which are of unusual 

 breadth ; the anterior ones show the effects of attrition depending upon the 

 position of the entire series in relation to those in the lower jaw, as shown in 

 the preceding specimen. Mtu. Brit. 



