1862.] OWEN REPTILIAN REMAINS. 239 



jS'o. 1, which Dr. Dawson supposes to belong to another individual 

 of Hylonomus, is figured of twice the natural size in PI. IX. fig. 5. 

 The bone, in respect to its proportions as to length and depth, 

 to the number, size, and shape of the teeth it contains, and to the 

 indications of sculpturing of the outer surface, resembles the maxil- 

 lary and dentaiy bones of Archegosaurus. A series of twenty-fou!* 

 teeth occupies a part of the alveolar border, a, 6 millimeters (nearly 3 

 lines) in extent ; but impressions and fragmentary traces of others 

 beyond show that there were at least 40 teeth in a row on one side 

 of the upper jaw. There is an indication of the lower border of the 

 orbit 0, above the hinder third of this series. The teeth increase 

 gradually in length as they approach this part ; their crowns are 

 slender, subcompressed transversely, pointed, but not sharply, with 

 evidence of alternate shedding. They are partially anchylosed to 

 shallow alveolar depressions on the border, towards the inner side, 

 of the jaw-bone. Their enamelled surface is smooth, and shows a 

 whiter colour than the bone itself. 



" Box No. 2. — Hylonomus aciedentatus, Dawson." 



This contains two portions of shaly carbonaceous matter. In one 

 is imbedded the major part of a maxillary bone (PI. IX. fig. 6), with the 

 inner side exposed, which is smooth, and demonstrates the fixation of 

 the teeth not to be as in the pleurodont lizard, but according to the 

 acrodont type ; the sockets, however, are shallow, and the simple bases 

 of the teeth are partially anchylosed thereto, as in Archegosaurus and 

 Labyrintliodon, and that of the largest tooth (being exposed by re- 

 moval of the inner alveolar wall) shows the fossa due to the matrix of 

 the successional tooth. The teeth are not so bent as to indicate which 

 is the front or which the hind end of this maxillary bone. The teeth 

 are the smallest at both ends, gradually increasing as they recede from 

 one end, and rapidly from the other, near to which are four or five 

 teeth, four times the length of the terminal ones of the series. I 

 suspect this to be the fore part of the bone. The proportions and 

 shape of the crown are much as in the Hylonomus Lyelli ; but there 

 seems to be a greater variety of length in the teeth of Hylonomus 

 aciedentatus. In both species the dentition indicates a small insecti- 

 vorous or vermivorous reptile. 



A second portion of coal-shale, in box No. 2 (marked 5 a), con- 

 tains the impression, with a small portion of one end, of a dentary 

 bone of the lower jaw, which held a series of at least 40 teeth 

 (PI. IX. fig. 7a). These, in size and proportion, agree with those of 

 Hylonomus Lyelli, in Xo. 1. The teeth very gradually decrease 

 from the middle to the two ends, especially to the anterior one. In 

 the number, proportions, and close arrangement of the teeth, this 

 dentary bone agrees with that of the Archegosaurus. Lizards have 

 not so many teeth. 



A third portion of coal (5 «), in box Xo. 2, contained the slender- 

 pointed end of a jaw-bone, with a close-set series of about 25 teeth 

 in an extent of 13 milHmoters, or 6^ lines (PL IX. fig. 9). These teeth 



VOL. XVIII. PART I. R 



