EASTMAN : CARBONIFEROUS FISHES FROM THE CENTRAL WEST. 171 
by Hancock and Howse over thirty years ago,} and more recently by Jaekel,? 
the latter author reaffirming the correctness of his predecessors’ conclusions. 
According to these writers, the strongly reflected, scoop-like extremity of the 
crown served for a cutting-margin, and the pavement-like, rugose, or imbricated 
portion as a triturating surface. This interpretation appears plausible enough 
in the case of some species, but must not be supposed to be of universal appli- 
cation amongst Petalodonts, very different conditions having existed in certain 
other genera. Teeth of Petalodus and Petalorhynchus have been found in 
successional series, the crowns overlapping and more or less erect (cf. Text-fig. 4), 
but it is not known how many of such series constituted the complete dentition. 
In these genera, as in Janassa, the median series are larger than the rest and 
bilaterally symmetrical, those of the lateral series more or less oblique. It was 
long ago observed by Hancock and Howse ? that Petalo- 
dus was provided with both symmetrical and oblique 
rows of teeth, and that examples had been “found 
lying in regular order, as if forming a portion of a 
vertical row.” Consequently we must express ourselves 
as at variance with Jaekel’s conjecture that the teeth of 
Petalorhynchus probably represent the symphysial series 
of Petalodus, their disparity in size and discordant dis- 
tribution clearly entitling them to recognition as distinct Wik 
genera. There are also excellent reasons for dissenting Pelalriimmehuspaittacs 
from his proposed union of Petalodus and Ctenoptychius, — yxs (M’Coy). Lower 
and from his theoretical association of the fin-spines Carboniferous; Ar- 
known as Stichacanthus and Physonemus (including magh, Ireland. Nat- 
Xystracanthus and Batacanthus), with Polyrhizodus and rally associated 
Petalodus respectively. Not only do the facts of dis- rata SEO 
ee Aae ies ; , : uter face, X 4. 
tribution militate with this last assumption, but the 
absence of fin-spines in Janassa renders it extremely improbable that such 
defencés were present in other members of the same family. 
It is inferred by Hancock and Howse from the fineness of the cutting-edge 
in two species of Janassa that the food must have consisted of soft material. 
They state of J. bitwminosa that “ the scoop-like cutting-margin is certainly 
much used, for it is almost always greatly worn in a regular manner ; only in 
one instance have we seen it a little broken. It would be an efficient instrument 
in cutting vegetable substances, and these might afterwards require the aid of 
the crushing-disk.” The presence of a carbonaceous mass in the abdominal 
region of certain specimens also suggests to them herbivorous habits. Jaekel, 
on the other hand, in discussing the probable food of the Permian J. bitwminosa, 
1 Hancock, A., and Howse, R., On Janassa bituminosa, Schlotheim. Ann. Mag. 
Nat. Hist. (4), Vol. V., 1870, p. 47, Pl. IL, III. 
2 Jaekel, O., Ueber die Organisation der Petalodonten. Zeitschr. deutsch. geol. 
Ges., Vol. LI., 1899, p. 258. 
®) Lee: Cii,-p. Ot: 
