Miss Agnes Crane — On Certain Living and Fossil Fishes. 211 
between tlie bony and cartilaginous types of fishes. The dentition 
is composed of a pair of voraerine teeth, and two molars in each 
jaw. The heart is three-cham bered, and true lungs exist with 
rudimentary extemal branchias and functional internal ones. 
Living Affinities of Lf.pidosiren. — Among living fish, the Lepi- 
dosiren is most closely related to another “ dipnoid,” discovered in the 
rivers of Queensland, Australia, in 1870. This species was at once. 
with singulär aceuracy, referred by Mr. Gerard K refft, the late Curator 
of the Sydney Museum, to Ceratodus, a genus tili then only known by 
the fossil teeth which occur abundantly in Triassic, and rarely in 
Oolitic strata. 1 He also described it “ as a giganticamphibian, and as 
allied to Lepidosiren,” the correctness of which determination has 
been fully demonstrated by the subsequent minute investigations of 
Dr. Günther 2 and Prof. Huxley, 3 who have published exhaustive 
memoirs on this subject. Two species of living Ceratodonts are 
recognized, one named after its discoverer, the Hon. William Foster, 
Ceratodus Fosteri, and Ceratodus miolepis, distinguishable only by its 
smaller and less ornate scales. These fish, known locally as “flat- 
heads,” inhabit the fresh and brackish waters of the Queensland 
rivers, and “ at night leave the streams, and go out on the flats, 
among the reeds and rushes, subject to tidal influence.” Dr. 
Günther is, however, of opinion that thev do not probably live 
freely on land, as the limbs are too flexible and feeble to support the 
heavy body, and considers that though they may be occasionally 
compelled to leave the water, they could not remain long in a lively 
condition without it. The species, which ränge up to six feet in 
length and twenty pounds in weight, appear to feed exclusivelv on 
the remains of plants Myrtacce and Gramina , taken in a decomposing 
state. The body of Ceratodus is covered with large cycloid scales, 
and the limbs are structurally identical with those of Lepidosiren, 
but the axis and fringe are more dilated, and the fin scales distinctly 
visible. The internal skeleton, though of a more cartilaginous type, 
resembles that of the mud-fishes, and the skull is partly osseous. 
The anterior nasal openings are situated under the lip, in front of 
the vomerine teeth, while the posterior pair are placed in the cavity 
of the moutb, a little before the maxillary ones. The dentition is 
essentially that of Lepidosiren, slightly modified to suit herbivorous 
diet, being adapted rather for “cutting and crushing” instead of 
“ piercing and cutting.” It consists of a pair of vomerine teeth, 
and two molars in each jaw, thus proving the correctness of the 
views of Pander and Agassiz, who had assigned that n umber of 
dental plates to the fossil forms of the middle geologic ages. The 
respiratory Organs are twofold, as in Lepidosiren, but the gills are 
more developed in Ceratodus, and when inhabiting clear waters the 
fish probably breathes by them alone, the true lungs only coming 
into action when on the mud flats, or living in turbid waters. The 
shape of the bodj', the number, position, and structure of the fins, 
1 Ceratodus Phitlipsi, Ag., Great Oolite, Mantell Coli., British Museum. 
2 Transactions of the Royal Society, 1871. 
3 Proceedings Zoological Society, IST 6, part i. June. 
