338 SIR R. OWEN ON A LABYRINTHODONT AMPHIBIAN. 
Hindostan, and 8. Africa, the batrachian type of air-breathing ver- 
tebrates had reached its highest development. 
If I were asked in terms of the present phase of “ conjec- 
tural biology,” “from what antecedent form the labyrinthie struc- 
ture of tooth had been derived,” I should reply that, in the 
matter of complexity, 1 know, at present, only the teeth of an 
extinct member of a lower class, characteristic of the Old Red Sand- 
stone, which are comparable. To the genus of fishes manifesting 
such dental character, the term Dendrodus is applied. For, here, 
a series of processes of the dentinal pulp radiates transversely to- 
ward the cement-clad superficies of the tooth-crown; but, in their 
course, they send off very numerous side branches which are soon 
resolved into tufts of dentinal tubules, suggestive of the generic 
name*. Processes of the cement-forming capsule also penetrate 
the dentine, but for a short distance only from the periphery, and 
there is no such interblending of the two tooth-tissues as in the 
great Triassic Batrachians. Between these and the Old Red Den- 
drodonts missing links, if such existed, are yet to be found. 
Of the extinct Reptilia enjoying life at later than Palzozoie 
periods, the Liassic Ichthyosaurs show convergence of processes of the 
dental capsule for a short distance into the substance of the base of 
the teeth, below or beyond the enamel-clad crown; but these con- 
verging processes are short and simple; and there is no reciprocai 
divergence oi dentinal productions of the formative pulp 7. 
DESCRIPTION OF PLATES XVI. & XVIL. 
Rhytidosteus capensis. 
Prate XVI. 
. Upper view of anterior part of the skull. 
2. Side view of the same. 
ra 
Ia 
Dm 
Prate XVIL 
Fig. 1. Under view of anterior portion of the skull. The above figures are 
reduced to two thirds of the natural size. ; 
2. Transverse section of a palato-vomerine canine, magn. 25 diam. 
* ‘Qdontography,’ Svo, 1840, p. 172, plate 62 B. 
t Ibid. p. 275, plate 73. In both labyrinthodont and dendrodont teeth the 
fractured surface usually displays a confused interblending of tissues, different 
from the simple compact dentine so exposed in saurian teeth. Observing 
this, Von Meyer remarked :—‘‘ Hochst merkwirdig ist die innere Struktur der 
Zabne von Mastodonsaurus; ich habe sie an einem dazu geeigneten Zahn- 
fragment in der Sammlung des Herrn Grafen Minster schon vor einiger Zeit 
erkannt.” Letter to Prof. Bronn, in ‘Neues Jahrbuch fir Mineralogie,’ &c., 
8vo, 1838, p. 15. No intimation of the nature of this structure is given. In 
the subsequent ‘ Beitrage zur Palzontologie Wirttemberg’s,’ 4to, 1844, my ex- 
position and term ‘ Labyrinthodont’ are accepted. 
