18 
POPULAR SCIENCE REVIEW. 
is of opinion that Ceratodus is not adapted to quit the water 
entirely, the limbs being much too flexible to support so heavy 
and unwieldy a body, and too feeble to be of much use in loco- 
motion on land. 
Ceratodus belongs to a most ancient order of fishes, and is 
represented in the Oolitic and Ehsetic beds, and in the Trias 
and Coal-measures, by fossil teeth almost identical with those 
of the living Australian lump-fish. 
Whilst dwelling on the persistence of embryonic characters in 
the adult, it is interesting to observe that in an extinct group 
of homocercal fish of the family Caturidse, (Woodcut, Fig. 15) 
characteristic of the Oolitic and Liassic periods,* all the species 
are homocercal and notochordal. 
Fig. 15.f 
Caturus furcotus , oolite, solenhofen (after Owen). 
p. pectoral; v. ventral; a. anal; d. dorsal; c. caudal fin. 
We have already pointed out that in the earliest shield- 
bearing fossil fishes of the Upper Silurian epoch, the Cephal- 
aspidse (Placo-Granoidei), there is no evidence whatever to 
show that they possessed any internal skeleton. They probably 
represented a group of fishes in which not only was the noto- 
chord persistent, but the neural and haemal processes were alike 
wanting, as in Amphioxus.% 
In the Chondrostei, represented at the present day by the 
Sturgeon ( Acipenser), the notochord is persistent, whilst the 
formation of the arches and their appendages does not pass 
beyond the cartilaginous stage. The head is covered by 
u ganoid ” plates, joined by sutures, whilst detached bony 
plates occur in rows along the body. (See Plate I., Fig. 6.) 
* Caturus similis, Agassiz, from the Chalk of Lewes, is a mere fragment 
of a jaw, to the determination of which no importance need be attached. 
t For permission to use this figure (reproduced from Prof. Owen’s 
1 Palaeontology,’ p. 163), we are indebted to the kindness of Messrs. A. & C. 
Black, Edinburgh. 
% Or the neural processes may have had a rudimentary development, as in 
the Lamprey ( Petromyzori ) ; Marsipobranchii. 
