212 Miss Agnes Crane — On Certain Living and Fossil Fishes. 
the elements of tbe internal skeleton, and above all the co-existence 
of a lang witb gills, sbow bow close is tbe affinity between the 
Australian Ceratodus and tbe mud-fishes of Africa and South 
America, and altbough the former approach less to the amphibian 
type than the latter, it is obvious tbat in a natural Classification tbeir 
place is side by side. 
Fossil Affinities of the Dipnoi. — Having shown tbe close 
connexion between tbe two genera of living dipnoids, let us 
now consider tbe relations of tbe living and fossil Ceratodonts. 
No remains of tbis genus bave as yet been found in the Tertiary 
or Cretaceous formations; but tbe fossil teeth, of wbich several 
varieties are recognizable, possibly the relics of numerous species, 
occur abundantly in tbe Triassic beds of Aust Cliff, near Bristol, 
and in tbe Muschelkalk of Germany. Tbey bave also been ob- 
tained from strata now determined to be of Triassic age at 
Maledi, south of Nagpur, in India, and associated, as in Europe, 
witb tbe reptilian remains Hyperodapedon. Many of tbese fossil 
teeth are much larger tban tbose of the existing species (specimens 
of one Triassic form measure over two incbes in length), and must 
necessarily bave belonged to individuals of a gigantic race. Tbe 
dental plates only bave been found fossil, but tbe structure of 
Ceratodus Fosteri indicates tbat tbey alone of a like-constructed 
animal would be susceptible of preservation in sedimentary strata, 
and tbe Classification of the recent forms witb tbose of tbe Mesozoic 
rocks, separated by so wide a gulf of geological time, thougb 
founded on tbe similarity of tbe dentition alone, is the only reason- 
able one, as there is no evidence tbat tbe living and fossil Cerato- 
donts, differed from eacb otber. Tbe teeth of tbis genus resemble 
in general shape and structure tbose of Ctenodus wbich are widely 
distributed in Carboniferous strata, species occurring in America 
being identical with tbose of tbe British rocks of contemporaneous 
age. Tbe dentition of the Devon ian Dipterus is also closely related 
to tbat of Ceratodus, as well as Lepidosiren. 1 
Tbus tbe bistory of tbe Dipnoi, an order before tbe discovery of 
the Australian Ceratodus only represented by tbe mud-fishes of Africa 
and South America, is carried back to remote geological ages, and 
tbe four living representatives, at present known, are found to be 
the survivors of a well-defined and characteristic group of fishes first 
appearing in tbe Devonian age. Tbey can be traced up from Dip- 
terus, through tbe Carboniferous Ctenodus, to tbe Jurassic Cerato- 
1 Prof. J. S. Newberry (vol. ii. Palteontology of Obio, p. 63, pl. 58, fig. 18) 
recognizes in bis new genus Heliodus, occurring in the Upper Chemung group of the 
American Devonian, the most gigantic member of the family of dipterine ganoids to 
which Ceratodus, Ctenodus , and Dipterus belong. The teeth resemble in microscopic 
structure those of Dipterus, and in general shape tbose of Ctenodus. The upper 
palatal ones differ, however, from those of all other known dipnoids in being united 
“in the form of a fully-opened fan.’’ He is also of opinion that the Palitdaphus 
insignis of Van Beneden and de Köninck, from the Carboniferous strata of Belgium, 
is not generically identical with the P. Devoniensis, of the same authors, and while 
admitting that the former is really a Plagiostome, considers that the latter should 
be associated with bis new dipterine genus under the designation of Reliodus 
Devoniensis. 
