On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain, 491 
‘being in a position too nearly perpendicular to render the ridged surface 
available. The teeth in both genera resemble each other much more than either 
resembles Myliobates, and except in the fact of the central tooth in each extending 
across the median division of the jaws, there could be little claim of relationship 
between the sharp, pointed, cutting teeth of the one, and the flat, extended plates 
of the other. In Myliobates and Zygobates each transverse row is composed of 
seven teeth, a largely expanded median tooth with three angular-sided flat- 
surfaced teeth on each side—a number which corresponds with that of Janassa, 
and in all probability with that of Petalorhynchus. 
From a careful consideration of all the external characteristics of Petalorhynchus 
and comparison with those of Petalodus the conclusion must be reached, that they 
possess generic features in common, and that whatever may ultimately be proved 
to be the zoological position of one of them, will, in all probability, be found to 
include the other. Whether this relationship will be found to extend also to the 
yaried genera which are included by Messrs. Newberry and Worthen in their 
definition of the Family Petalodontidee may be doubtful. The genus Janassa 
(including Climaxodus, M‘Coy) which has been shown to possess characters closely 
associating it with that of Petalorhynchus, will also be found to form one of the 
same family. This appears to have been to some extent foreseen by Messrs. 
Hancock and Atthey, who state that®* “ Ultimately, perhaps, Petalodus will be 
found to be more closely related than can at present be demonstrated (.¢., to 
Janassa), for it is not only in the Petalodontoid form that a resemblance is 
observed, but likewise in the primary teeth themselves, which show a remarkable 
similarity in general form to some of the Petalodontes.” And in a second paper 
“On Janassa bituminosa, Schlotheim, from the marl slate of Durham”t by Messrs. 
Hancock and Howse, the concluding paragraphs are, “It is unnecessary here to 
dilate on the affinities of Janassa. We may remark, however, that the full 
investigation of the Permian Species has only the more confirmed our opinion of 
‘ts close alliance with the coal measure form (the so-called Climaxodus lingueformas), 
and of a certain relationship of both to Myliobates and Zygobates. We may also 
state that Janassa is more closely related to Petalodus than was at first thought ; 
for we now find that the latter genus is provided with both symmetrical and 
oblique teeth ; so that it is quite probable that they may be found to be arranged 
in much the same manner as those of Janassa, especially as the former have been 
found in vertical series, as previously stated.” 
It thus appears that a close relationship exists between Petalodus of the 
Mountain Limestone, Petalorhynchus of the Yoredale Rocks, Climaxodus from the 
Coal Measures, and Janassa from the Permian Rocks, and that the latter, whilst 
agreeing in the main with the genera of the older formations, also possess some 
* (Op, Cit.,” p. 335. + « Op. Cit.,” p. 356. 
