On a Reptilian Tooth with two Roots. DIF. 
EXPLANATION OF PLATE IV. 
Fig. 1. Body of animal from above, somewhat flattened. 
Fig. 2. Ditto from the side. 
Fig. 3. Head viewed from the left front. a.a.= first antenna. 
Fig. 4. Last segment of abdomen from below. 
Fig. 5. Abdomen from below, showing the opercular plates. 
tig. 6. One of the legs. 
XXXVII.—On a Reptilian Tooth with two Roots. 
By H. G. Seexey, F.R.S. 
THE division of the root of a mammalian tooth into two or 
more portions has been regarded as a convenient means of 
predicating mammalian organization for the animal in which 
this condition is found, notwithstanding the circumstance 
that in diverse groups of mammals the root is not divided in 
any of the teeth, and that in mammals the division is absent 
from the incisors and almost all canines. 
Professor Marsh, in 1890, figured, in the ‘ American 
Journal of Science,’ teeth of the animal which he named 
Triceratops, in which two roots certainly occur, but placed 
transversely, as sometimes happens among the wider posterior 
molar teeth of mammals. It is not improbable that this 
division, as American paleontologists have suggested, is 
apparent rather than real, and has been produced by absorp- 
tion of the tooth in wear, by the successional tooth rising 
beneath it, since the form of the excavation between the roots 
exactly corresponds to the form of the crown. In any case, 
the condition in this American fossil, by whatever name the 
genus may be eventually known, was unparalleled among 
Reptilia, though in a few mammals with two roots to a poste- 
rior molar tooth. those roots are arranged transversely. 
In 1854 (Quart. Journ. Geol. Soc. vol. x. p. 420) the late 
Sir Richard Owen figured a Purbeck fossil from bed K. 93 
in Austen’s guide, under the name Nuthetes destructor. It 
was then described asa pleurodont lizard allied to monitors of the 
genus Varanus ; and figs. 2 d and e (/. ¢.) are representations 
of teeth in the jaw which have the aspect of possessing two 
roots arranged in the antero-posterior direction. ‘This con- 
dition is further evidenced by the enlargement of the tooth d 
given in fig. 4, though no word occurs in the text referring to 
the structure ; so that it is probably only a pit or groove at the 
base of the crown. With these fragments of jaw the author 
