Teeth in the Centetide. 537 
the milk-dentition than in the permanent set. This applies 
on the whole to the same teeth in the lower jaw also, as well 
as to the milk-premolars. Moreover, before proceeding to 
discuss the facts of the case somewhat more in detail, I would 
premise, by way of a general observation, that in the Cente- 
tide there is rather less difference between the accessory and 
the main cusps (the former being more, the latter less 
strongly developed) in the milk- than in the permanent 
dentition, 
1. Upper Jaw.—The least divergence in form between the 
premolars and molars is found in Heh¢nops, the premolars 
of which differ to an extraordinary degree from those of 
Oryzoryctes hova, which in this respect forms the opposite 
extreme. ‘The closest approach to Hchinops is exhibited 
by Hriculus. 
In Echinops and Ericulus, P.1 (Hens.) is hardly dis- 
tinguishable from M.1; the difference from the molars—and 
from P.d.1—to be discussed later on, in the position and 
height of the antero-external cusp, is demonstrable only in 
teeth which are intact. In both genera P.1 is somewhat 
longer than M/.1, and in Echinops it is also somewhat 
breader (in the transverse direction) than the premolar of 
Ericulus ; in the former there is found a low “ protocone ” 
and “ hypocone.”’ 
In Ericulus P.2 already assumes the form of a carnassial ; 
this is much less the case in Hchinops, in which the same 
tooth is as yet more like a molar, since here the antero- 
external cusp does not extend so far forwards, and the whole 
tooth appears altogether less elongate than P.2 and P.d. 2 
of Hriculus (I am not acquainted with P.d. 2 of Echinops). 
P.2 of Echinops has in addition a distinct internal cusp 
(“‘ protocone’’), and that of Hriculus has two such cusps like 
P.1 of Echinops. 
P.3 of Echinops resembles a carnassial; but the antero- 
external cusp is very slightly marked. ‘Three roots are 
present, and the inner one bears a fairly large internal cusp. 
‘The milk-tooth agrees with its successor in form. 
In comparison with P.3 of Hchinops, the corresponding 
tooth in Ericulus is somewhat reduced, and the secodont 
form begins to be seen: the longitudinal diameter is the 
greater, while in Hchinops the transverse expansion is the 
more pronounced. There are but two roots. A feebly 
developed basal margin, as the remains of an internal cusp, 
is confined to the posterior half of the inner side. A rem- 
nant of the external cusps, likewise limited to the posterior 
half of the tooth, is present, as well as in many cases a 
Ann. & Mag. N. Hist. Ser. 6. Vol. xx. 36 
