Mammalia. 53 



one and two teeth, being in fact a single root with two crowns. 

 The remaining teeth differ markedly from tlie corresponding teeth of 

 Ko. 43.11.25.4 in that only one of them is distinctly double- 

 rooted. The bifurcation of the root is represented in the remainder 

 merely by a slight basal notch, most prominent in the last tooth on 

 the left side, and by a central groove which, passing up each side of 

 the root and being deeper externally, evidently represents the double- 

 rooting of the cheek-teeth of No. 43.11.25.4. The groove is so 

 prominent in the last tooth on the right side that this tooth is 

 double-rooted, although not so prominently so as is the corresponding 

 tooth of No. 43.11.25.4. 



The teeth of the lower jaw in 324i represent in various degrees 

 the steps between single- and double-rooted teeth. Each of the first 

 pre-molars is double-crowned, but single-rooted, like the first tooth 

 on the right side of the upper jaw. The second and third teeth 

 on each side possess a broad, compressed, single root, divided by a 

 rather deep, central, longitudinal groove on each side. The fourth 

 and fifth are distinctly double-rooted, but not so prominently as 

 are the corresponding teeth of No. 43 . 11 . 25 . 4. 



Of the two ' Belgica ' skulls, No. 897 agrees, in the number of its 

 cheek-teeth and the character of their roots, with No. 43, 11, 25, 4. 

 The teeth, however, especially the low^er incisors, are rather small. 

 No. 700, on the other hand, presents us with an entirely new 

 combination. In this head there are six teeth on either side of the 

 upper jaw, but liere, if we are to apply the same hypothesis as 

 before, the splitting process has apparently taken place not at the 

 anterior, but at the posterior, end of the series. Thus the two last 

 teeth on either side are much smaller than the remainder, and 

 may be taken to represent the fifth tooth of a normal head. The 

 first of the pair is in each case double-rooted ; the second is single- 

 rooted on the left and imperfectly provided with two roots on the 

 right. The remaining teeth of the upper jaw are similar to those of 

 No, 43, 11, 25, 4, except only that the double root of number two is 

 very feebly developed and the small basal notch runs up the tooth as 

 a groove as in No. 324&. In the teeth of the lower jaw we have 

 every gradation, from the tapering single-rooted number one, 

 through the flattened and grooved number two, and the slightly 

 double-rooted number three, to numbers four and five, both double- 

 rooted, and with, in the latter case, widely separated fangs. 



The four specimens brought home by the 'Southern Cross' are 

 invaluable as presenting us with further modifications of the same 

 type of variation. All are adult, but not one of them agrees with 



