68 Chajwum (trid Fi-itrlntrd : 



In addition to the above, we have a large number of more 

 or less imperfect palates from which the average number of 

 plates in the jjile was more accurately determined than might be 

 judged from the above table, and the proportion of incomplete 

 to complete specimens we would estimate at subout three to one. 



The relatively greater abundance of the upper jaw as com- 

 pared with the lower may be due to the fact that the lower jaw 

 soon falls away from the fish after death, and thus runs a greater 

 risk of destruction before coming under the influence of sedimen- 

 tation, and consequent preservation of the remains. 



Locality and Horizon. — Grange Burn, Western Victoria, from 

 the nodule bed at the base of the Kalimnan (Nat. Mus. Coll., 

 purchaised R. Lindsay ; also 2 fine specimens of upper jaws pre- 

 sented by A. A. Kelley ; also Spry Coll. and Pritchard Coll.). 



Beaumaris, Port Phillip (Nat. Mus. Coll. specimens collected 

 by the late W. Kershaw, several presented by J. A. Kershaw, an 

 exceptionally fine upper jaw presented by C. P. Smart, a lower 

 jaw presented by the late J. F. Bailey and 8 specimens pur- 

 chased from W. B. Jennings ; also Pritchard Coll., including an 

 extensive series of small specimens ; and Dixon Coll., which has 

 yielded the largest specimen). — Base of the Kailimnan. 



01)servations. — The palatal aspect of the upper jaw shows the 

 fossil form to be more angularly pointed at the beak than in the 

 living D. hystrix, L., and more nearly approaching D. blochii, 

 Casteln.. both of which species occur in Port Phillip, the latter 

 beinir the commoner. Lateral margin less curved and more 

 widely divergent tha,n in the living forms, the marginal denticles 

 being generally coarser, averaging ten on each side, whilst our 

 recent forms have twice that number. There is also a greater 

 tendency in the full-grown fossil forms to an extension of the 

 excavated area between the palatai plates and the denticulated 

 oral margin. 



It appears that the recent form D. hystrix occasionally at- 

 tained dimensions nearly equal to that which is indicated by 

 the size of the jaw in the fossil species, since one individual 

 is recorded from the British Museum Collection^ which has a 

 length of thirty inches, but this is exceptional. Giinther- men- 

 tions the largest form as attaining a length oi two feet. 



1 Cat. Fishes ISrit. Mus., vol. viii., 1870, \>. 31IU. 



2 -An Inti'oductioTi to tliu Study of Fishes, ISSO, p. (iSi). 



