﻿Miss Agnes Crane — On Certain Living and Fossil Fishes. 211 



between the bony and cartilaginous types of fishes. The dentition 

 is composed of a pair of vomerine teeth, and two molars in each 

 jaw. The heart is three-chambered, and true lungs exist with 

 rudimentary external branchige and functional internal ones. 



Living Affinities of Lepidosiren. — 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 singular accuracy, referred by Mr. Gerard Krefft, the late Curator 

 of the Sydney Museum, to Ceratodus, a genus till then only known by 

 the fossil teeth which occur abundantly in Triassic, and rarely in 

 Oolitic strata.^ He also described it " as a gigantic amphibian, and as 

 allied to Lepidosiren," the correctness of which determination has 

 been fully demonstrated by the subsequent minute investigations of 

 Dr. Gunther'^ and Prof. Huxley,^ who have published exhaustive 

 memoii^s on this subject. Two species of living Ceratodonts are 

 recognized, one named after its discoverer, the Hon. William Foster, 

 Ceratodus Fbsteri, and Ceratodus miolepns, 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. 

 Giinther is, however, of opinion that they do not probably live 

 freely on land, as the limbs are too flexible and feeble to sujDport 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 range up to six feet in 

 length and twenty pounds in weight, appear to feed exclusively on 

 the remains of plants Mi/rtacce and Gramince, 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 tj^pe, 

 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 mouth, 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 Aeassiz, who had assigned that number 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 body, the number, position, and structure of the fins, 



1 Ceratodus Phillipsi, Ag., Great Oolite, Mantell Coll., Britisli Museum. 



- Transactions of the Royal Society, 1871. 



^ Proceedings Zoological Society, 1876, part i. June. 



