MAMMALS COLLECTED IN SIAM. 389 
of the zygomata, lower part of the cranium, basioccipital and bullae), 
skulls are essentially similar, but on the whole the nostrils are less 
acutely pointed behind ; the postorbital processes do not quite touch 
the cranium posteriorly, though in one example there are indications 
that contact might occur ; the palatal foramina are narrower and the 
palate bridge broader. The anterior feet of the zygomata are well 
expanded ; the basioccipital is very variable in shape and cannot be 
relied on for purposes of differentiation. 
As regards the teeth the incisor groove in peguensis (type) 
is essentially bifurcate, with the outer branch again forking !; in the 
series of siamensis the groove is well-filled with cement but is 
extremely variable otherwise. In the leveret (No, 2402) it is bifur- 
cate, but in older animals the evolution can be clearly traced (Nos. 
2532, 2124, 2444, etc.) of the three-branched pattern found in other 
individuals which is probably typical (Nos. 2445, 2123, 2122). The 
most eastern and southern specimens exhibit, on the whole, a much 
more complicated groove than the others, as they have four, and 
even five, branches (Nos, 2536-8, 2105) 
The .present series, though it does not come from one place, 
is undoubtedly of one form only, and serves well to illustrate 
Forsyth-Major’s conclusions? :—“ Specimens of the same species 
may vary slightly owing partly to individual variation. But the 
shape of the enamel fold varies equally at different stages in the 
age of the animal; species whose incisors show the most complicated 
pattern in the adult have as yet no trace of this in very young 
annimals; and vice versa in very old specimens complication tends 
to disappear again. As shown by several of the text-figures, slight 
variations between the right and left incisor of the same individual 
also occur.” 
The incisor groove is a feature that can only be depended on 
within wide limits for separation of different forms. 
Lepus siamensis does not seem to differ markedly from 
L. peguensis, and is distinguished by the absence of any white on 
1 vide Records of the Indian Museum, XV., p. 92, fig. 11 (1918). 
2 Trans. Linn. Soc, VII, Zoology, p. 466. (1899 ). 
VOL. 111, NO. 4; 1919; 
