1869,| HULKE—KIMMERIDGE ICHTHYOSAURIAN(?) TEETH. 173 
dentine, coated with a thin layer of enamel. The dentinal tubules 
pass straight from the pulp-cavity towards the enamel without 
Waving, in which respect, and in the almost complete absence of 
the concentric granular rings, which are so conspicuous a feature in 
the dentine of many crocodilian teeth, the dentine of these teeth 
resembles that of the unfluted apex of an Ichthyosaurian tooth-crown. 
The enamel, however, is thinner than that of several sections of 
Liassic Ichthyosaurian teeth of about the same diameter. At the 
base of the fang the dentine, owing to the presence of a large pulp- 
cavity, becomes thin; and its contour is here slightly and irregu- 
larly indented, but the indentations are quite insignificant in com- 
parison with the deep inflexions which distinguish the tooth-fang in 
Ichthyosaurus. The pulp-cavity extends into the base of the crown. 
‘Its apex is filled with spar; and its lower end contains a plug of 
ossified tooth-pulp, continuous through the open end of the cavity 
with the external cementum, its vascular canals freely inosculating 
with those of the cementum in this situation. The vascular canals 
of the cementum are large and numerous. Their principal branches 
take the direction of the long axis of the fang, running from the 
base towards the neck. The bony tissue channelled by them 
abounds in lacune, which do not differ in any essential particular 
from those of the bones which bear the teeth. 
The connexion of the teeth with the jaw appears to resemble that 
which obtains in Ichthyosaurus: they are neither soldered to a flange 
nor implanted in sockets, but they are arranged in a line in an open 
groove in the upper surface of the jaw. Several of them are dis- 
placed out of the groove, which shows the absence of anchylosis to 
the dentary bone, and that they were attached to it only through 
the medium of the soft tissues. Of the teeth remaining i situ, six 
occupy 1:5 inch. 
The swelling caused by the great development of the cementum 
gives these teeth some resemblance, but only of a superficial 
kind, to those of the Chalk “ Fossil Fish or Reptile” lately pur- 
chased by the British Museum, formerly in the collection of Mr. 
Toulmin Smith, who described it in Charlesworth’s ‘ London Geo- 
logical Journal,’ No.1. Sept. 1846. My. Bowerbank afterwards re- 
ferred to it in a paper on bone corpuscles. The teeth are here in- 
serted in bony cups; and Mr. Smith expressed the opinion that 
these were shed together with the teeth. The occurrence of gaps 
in the dentary series from which both cup and tooth are absent pro- 
bably led to this view ; but there are also several full-sized empty 
cups without tecth in them, which demonstrates that the cup and 
tooth do not in every instance simultaneously disappear, and ren- 
ders it very unlikely that any hard stractural connexion existed 
between them. I think it more probable that the tooth was gene- 
rally first shed, or detached by violence, and that after this the cup 
was remoyed by the abrasion of its thin unprotected edge, and by 
absorption. 
As well asI can judge, in the absence of sections through the 
tooth-cup and bone which bears it, the cups are upgrowths from the 
