CLASSIFICATION OF DEVONIAN FISHES 435 
upper; the scales are cycloid. Thus far, in fact, the definition of 
Ctenododipterini agrees with that of the Glyptodipterini; but the 
former differ from the latter in the smoothness of their scales; in 
the structure of the roof of the cranium, whose constituent bones are 
anchylosed into a singular shield, presenting some resemblance to 
the cephalic shield of <Accipenser; and lastly, and chiefly, in the 
peculiar form of the lower jaw, which much resembles that of 
a Ccelacanth, and in their dentition, so well made known by Hugh 
Miller, whose researches have been fully confirmed by Professor 
Pander. 
In the next place, the true CC@ELACANTHINI have ano less well- 
defined right to occupy a similar position! I say the ¢7we Ccelacan- 
thini, because the term “Ccelacanth” has been used by different 
Fig. 10.? Déipterus. 
paleontologists with such very different meanings, has been made 
in some cases to include so much, and in others to include so little, 
that I feel it to be necessary to define precisely the sense in which 
I employ it here. I intend it, then, to designate that family of 
fishes of which the genus Celacanthus of Agassiz is the type, a 
family which, thus restricted, is as well defined and natural a group as 
any in the animal kingdom, but, at present, can embrace only the 
genera Calacanthus, Undina, and Alacropoma. 
1 Several years ago Sir Philip Egerton strongly drew my attention to the close affinity 
between the Calacanthini (mth) and what I have termed the Ghiptodiplerini, particularly 
showing the importance of the lobate paired fins and of the double dorsals common to the genera 
of both families (which Sir Philip Egerton was inclined to group under the one head of 
‘ Celacanths’), and illustrating his views by a synopsis of the genera. From the study of that 
synopsis I trace the gradual clearing up of my own ideas respecting the difficult subject with 
which this preliminary essay attempts to deal. 
2 The woodcut, fig. 10, represents the same specimen as that figured by Sir Philip Egerton 
in “Siluria,” ed. 2, p. 287, but of the natural size. It exhibits the characters of the paired 
fins of Diplerus remarkably well. 
BZ 
