56 Prof. Owen— On a New Saiiroid Fish. 



longitudinal dent or notch, as if from the effect of a bruise, at the 

 middle of the outer side of the base : and this is more marked, or is 

 longer, in the lower than in the upper laniaries. It occurs in that 

 part of the dentine which was covered by cement, and is, I believe, 

 made more conspicuous in the specimen (Plate III.) through the loss 

 of part of that outer coating. Not more than one-half of the crown 

 is coated with enamel. This apical half give's a more circular trans- 

 verse section than the cement-covered basal half. The enamel is 

 marked by fine longitudinal striee, with a few similar ridges. The 

 teeth in which this part is preserved attain almost the length of an 

 inch, with a basal breadth of half an inch ; but the dimensions of 

 all the parts are shown in the figure, accurately drawn of the natural 

 size. The margia of the hollow base of the cement-covered part 

 was anchylosed by that bone-like tissue to the border of the alveolar 

 depression. The maxillary teeth are rather larger than the pre- 

 maxillary ones. 



The outline of the alveolar part of the upper jaw was undulated 

 as in the stronger-jawed species of Crocodile, that of the pre- 

 maxillary (^-) and maxillary (-^) describing a convex curve where 

 the strongest teeth are fixed, with an intervening concavity. On 

 both sides of the mouth two of these teeth are close together at the 

 middle of the maxillary convexity (-^) ; the same disposition marks 

 the three larger teeth at the alveolar convexity of the premaxillary. 

 Other laniaries are separated by intervals equalling the basal breadth 

 of the tooth, or exceeding it, as where the contiguous teeth of the 

 maxillary and premaxiliary descend into dental interspaces of the 

 lower jaw. The density of the bone increases as it recedes from the 

 alveolar part. The upper convex border of the maxillary is smooth 

 and polished, like ivory ; the outer surface of the adjacent bone is 

 roughened by raised strise, running mostly in an oblique direction 

 downward and forward. All the outer surface of the dentary 

 element (PL III. ^-) of the lower jaw is finely striated, save at the 

 irregularly thickened part of the lower border of the bone. The 

 right dentary (ib. ^^') being slightly dislocated downward, exposes 

 the flat inner surface, which shows the coarser longitudinal fibres 

 of the osseous texture there. I cannot detect any evidence of an 

 inner series of teeth, added to the outer row of large laniaries in the 

 lower jaw of TJilattodus : there may have been a few small scattered 

 ones, if these have not fallen from the palate. 



A single detached tooth of the genus may be distinguished from 

 any of those similarly-sized Sauroid Fishes which have come under 

 my notice ; as, e.g., by the squarer form of the basal half, and rounder 

 shape of the aj)ical half, of the crown, from the tooth of the Cretaceous 

 Saurodon,^ Saiiroceplialus,' and SauricJithys,^ from the tooth of the 

 Liassic and Lower Oolitic Eugnatlius,^ from that of the Carboniferous 

 MegalicJitliys, etc. The above-described shape and strong outer 

 notch co-exist, indeed, so far as I know, only in the Upper Oolitic 



1 Dixon's "Geology and Fossils of Sussex," 4to. 1850. PI. xxxii. 



2 Ibid., PL XXXV., fig. 5. 



3 Agassiz, '• Eecherches sur les Poissons Fossiles," Tab. 55a. * lb., Tab. 57«. 



