154 Sir J. W. Dawson — On Dendrerpeton Acadiamim, etc. 



cephala of the Gas-coal of Bohemia, has some valuable remarks on 

 the affinities of these animals ; and, though I can by no means agree 

 with the manner in which he arranges them in families, or with 

 the way in which he mixes up Labyrinthodontia and Microsauria 

 with other creatures so different as the Branchiosauridse and the 

 Ophiderpeton group, I think his conclusions deserve mention, and 

 may state them nearly in his own words as follows: — 



After remarking on the fact that we know no clear links of 

 derivation from any previous animals, he states that on any theory 

 of derivation different origins must be supposed. He illustrates 

 this by the characters of the vertebrae in different genera, as, for 

 instance, the biconcave, the partly cartilaginous, and the diplo- 

 vertebrate types. 



Whatever view may be taken of their origin, the increased 

 knowledge of their structures has not made clear as yet their 

 precise relation to modern Amphibia and Reptilia ; and only serves 

 to make us doubt whether the distinctions recognized in the modern 

 forms apply to these ancient creatures in the same degree. We 

 seem indeed to have, both in the Labyrinthodonts and the Micro- 

 saurians, composite or generalized types having properties akin to 

 those of both classes, and these in very different degrees. If we 

 regard them all as agreeing in the general structure of the skull, 

 with its free parasphenoid, and a similar set of bones in the 

 shoulder-girdle, then we shall find that in other respects we have 

 a heterogeneous assemblage, some agreeing in the formation of the 

 vertebrge, ribs, and pelvis, with Amphibians, others with Eeptiles ; 

 and there are corresponding differences in the dermal covering. If 

 we attempt to group these creatures in orders and families, we are 

 met with very great difficulties, owing to the variety and kinds 

 of their differences, which, in connection with the imperfection of 

 the material, almost defy the classifier. 



So far Fritsch, and 1 may add that I consider that little is gained 

 by grouping animals so diverse in organization under one head of 

 Stegocephala in consequence of resemblances in certain cranial bones, 

 and that a more general and large view should be taken of the tout 

 ensemble of their structures. 



With reference to that selection of these animals which has been 

 preserved in the erect trees of Nova Scotia, the only ones which 

 it has been necessary for me to study, I have no hesitation in 

 placing in two orders or families, that of the Labyrinthodontia, to 

 which Dendrerpeton belongs, and that of the Microsauria, including 

 Eylonomus, Eyierpeton, Fritschia, and Smilerpeton, all of which have 

 many important points in common. The other forms I leave to 

 those who have to deal with them, but I feel convinced that some 

 of them should be separated, probably ordinally, from the above. 



The following extract from Credner on the systematic position of 

 Hyloriomus and Petrohates, shows that he to some extent shares in 

 these views.^ It should be understood, however, that his Eylonomus 



^ Zeitsch. Deutsch. geol. Gesellsch., Berlin, 1890, p. 257. 



