132 R. Etheridge. 



4. — Opalised Reptilian Dentary from Lightning Ridge. 



(PI. 8, figs. 10 and 11). 



To Colonel R. E. Koth, D.S.O., M.R.C.S.E., the Australian 

 Museum is indebted for sundry reptilian and molluscan remains; 

 from the above locality. The most attractive of these is a small 

 dentary (PI. 8. figs. 9 and 10), posteriorly broken just at the 

 symphasis, and incomplete forward. There are six teeth set in 

 sockets in an alveolar groove, and supported by the outer alveolar 

 wall, in other words, a pleurodont dentition; the entire specimen is 

 one and three-quarter inches long, the bony tissue being wholly 

 converted into ordinary blue-black opal. 



The most complete tooth measures five millimetres from the bottom 

 of the alveolar groove to the tooth apex, but at what I take to be 

 the posterior end of the specimen, the socket visible there is quite 

 ten millimetres deep, and as the slightly curved teeth extend to the 

 bottom, it follows that some of them, at least, attained a length of 

 fifteen millimetres; at the anterior end the alveolar groove is 

 shallower, about six millimetres, the bone itself has a maximum 

 width of fifteen millimetres. The teeth are faintly striate to about 

 the middle of their exposed length, and opalisation has removed all 

 trace of osseous structure throughout the specimen. 



Our present knowledge of the Australian Cretaceous reptilian 

 fauna is a very limited one. A few Iclithyopterygian and Saurop- 

 terygian remains, a Chelonian or two, a Saurischian {Agrosaurus 

 macgillivray), Crocodilian scutes, and other dermal scutes of an 

 unknown reptile,^ possibly Stegosaurian, about complete the list. 



In looking round for relatives of this very beautiful little fossil, I 

 was at first led towards the Ichthyopterygians, but being unsuc- 

 cessful in this direction, I took the precaution of consulting my 

 former colleague, Dr. Smith Woodward, who suggested a provisional 

 reference to the American Cretaceous and imperfectly known genus 

 Botosaurus, L. Agassiz. There is certainly a resemblance to Leidy's 

 figures, but there are also discrepancies in the form of the teeth 

 which it will be well to point out. 



In Botosaurus harlani, Leidy said that one of the teeth had a 

 mammiliform crown and a gibbous fang; another, the penultimate 

 or last tooth possessed a laterally compressed mammiliform crown, 



1 Etheridjfe. Rec. Austr. Mus., v., No. 2, 1904. 



2 Leiily : " Cretaceous Reptiles of the Uiiiteil States." Smithsonian C'oiitrih. Kiiowledsre, 192,. 

 1865, p. 12. 



