? EQUUS ZEYLANICUS. 277 
further remark save that its size (74 mm. outside curve, 
13 mm. widest part, and 42 mm. greatest circumference) 
declares its possessor to have been a stallion, weighs 8°19 
grammes.* When due allowance is made for unequal wear, 
certain peculiarities, more or less distinctive of the Wellawatta 
molar, are to be noted ; these, together with the corresponding 
characters of H. leptostylus and EH. caballus, are set forth in 
tabular form below. 
The first ten characters of the upper left P. M. 4 of 2. 
leptostylus are taken from Hikoshichiro Matsumoto’s descrip- 
tion, while the others under the same heading are to be 
observed in the plate accompanying the same publication. In 
Plate I. of this paper the more important structures of the 
teeth are drawn to a magnification of two diameters. 
In no instance is there complete agreement between the 
three teeth. 
With regard to one character (16), (B) and (C) are alike in 
their difference from (A); in three characters (1, 2, and 7) 
(B) approaches (C) more closely than it does (A); in four 
characters (4, 5, 6, and 12) (B) is more or less intermediate 
between (A) and (C) ; in six characters (3, 8, 9, 10, 11, and 15) 
(B) shows more resemblance to (A) than to (C); while in two 
characters (13 and. 14) (B) is peculiar. 
The upper left last premolar of #. leptostylus is more akin 
in structure to the first upper left molar of #. caballus than 
it is to its homologue in the latter species, inasmuch as last 
upper left premolar of the modern horse is longer in proportion 
to its width and has more marked and more complicated 
plications than either the corresponding tooth of Z. leptostylus 
or its own first molar. On the other hand, the Wellawatta 
cheek tooth resembles the collateral grinder of E. caballus 
more closely than it does any other tooth of the modern 
horse. What degree of correspondence exists between the 
upper left first molar of 2. leptostylus and the upper left first 
molar of #. caballus we do not know, but we see from analogy 
that the plications of the former were simpler than those of 



* One of the minor difficulties of the “‘ cavern” theory was to 
explain how two teeth of such very different size and weight should 
have remained together during the movements of the mud stream. 
15 6(9)16 
