Woodward— Crustacean Teeth. 403 
that Dr. Giinther at first sight supposed them to be Fish-teeth 
allied to the Spheride or Labride; whilst Prof. Owen and Mr. 
Waterhouse, to whom they were submitted for inspection, noticed 
their great superficial resemblance to the teeth of some small Mar- 
supials, such as the Kangaroo Rat (Hypsiprymnus) of Australia. 
The important bearing of these ‘ superficial’ resemblances cannot 
be too strongly impressed upon Paleontologists, and especially on 
those who work in that Border-land between the Palzozoic and 
Secondary rocks—the Rhetic and Triassic groups. For it was in the 
Rheetic Bone-breccia of Wiirtemberg that Prof. Plieninger discovered 
the teeth of the then oldest known Mammal, the Wicrolestes anti- 
quus ; and in a fissure of the Carboniferous Limestone near Frome, 
Mr. Charles Moore, of Bath, found that wonderful accumulation of 
minute teeth and other organic remains from a Bone-bed of the same 
age; and Mr. Boyd Dawkins detected the tooth of the oldest British 
Mammal (the Hypsiprymnopsis Rheticus) in the Lower Rhetic of 
Watchet. These teeth, all very minute, often very obscure, require 
the closest scrutiny, and wherever it is practicable their structure 
should be microscopically examined. 
In the Mammalia the molar teeth are all provided with double 
roots or fangs; there is also a well-marked division or ridge which 
surrounds the base of that part of the tooth which is exposed above 
the gum—a character which distinguishes them from those of Fish 
and Reptiles. But if the crown only of the tooth of a small fossil 
Marsupial be compared with a part of one of these gastric teeth of 
Dithyrocaris, these characters will scarcely suffice to distinguish 
between them, and we must examine their more minute structure. 
In the plate I have given figures (13 and 13 a, 6, c) of the teeth 
of a young Kangaroo (Macropus) for comparison with the enlarged 
figure (fig. 3b) of the tooth of Dithyrocaris, which will serve to show 
many superficial points of form which they possess in common. 
Fig. 10 is the recent Apus (from near Prague in Bohemia), of the 
natural size, for comparison with Dithyrocaris and Ceratiocaris 
. (figs. 1 and 9). Fig. 11 is an enlarged view of the same, showing 
the jaws (a, a) in sité ; whilst figs. 7, 7 a, and 7 6, represent these dis- 
sected out, and magnified about seven times. There is a consider- 
able difference between the serrated mandible of Ceratiocaris and 
the more solid and massive teeth of Dithyrocaris; and among these, 
also, there are at least two distinct forms: but we need more mate- 
rials before we can determine to which species these several forms 
of teeth belong. 
EXPLANATION OF PLATE XI. 
Fig. 1. Ceratiocaris papiho, Salter. U. Ludlow Rock, Lanark. 
2. C. papilio, Salter. Detached jaw from same locality 
3. Nearly perfect tooth of Dithyrocaris, Upper Marine series, Orchard 
Quarry, Thornliebank, Renfrewshire. 
3 a. Side view of same. 
3 6, Enlarged view of grinding surface of same, showing the fine strice 
in the recesses of the C-shaped cusps. 
DD 2 
