193. EXTINCT SHARKS AND GANOID FISHES. 437 
cartilages of their limbs excessively abbreviated. It is, however, 
stranger still to have to regard the Paleoniscide as primitive repre- 
sentatives of the modern sturgeons; and yet Dr. Fritsch, following 
all who have deeply studied the subject, is fully convinced of the 
necessity of this course. He describes the genus Tvissolepis, giving 
the restoration copied below; and this he regards as the type of a 
distinct family to be placed in the same sub-order as Palg@oniscus 
itself. 
The Paleoniscide, as a general rule, conform to the type shown 
in Fig. 2; being essentially sturgeons (as Dr. Traquair first pointed 
out) covered with regular rhombic scales and provided with a complete 

Fic. 2.—Restoration of Palgoniscus macropomus ; Permian, Germany. 
(After Traquair.) 
gill-covering apparatus. In some cases, however, the scales disap- 
pear except on the upper lobe of the tail; and in a single instance, 
briefly noticed by Dr. Traquair, the scales become deeply over- 
lapping and almost or quite cycloidal. 
Now, the great interest of Dr. Fritsch’s new contribution to the 
subject consists in the fact that it is the first detailed and illustrated 
account of one of these ancestral sturgeons possessing cycloidai 
scales. Moreover, it is to be noted that in T7vssolepis the cycloidal 
scales are confined to the trunk, while the rhombic scales persist on 
the upper lobe of the tail. One and the same fish thus displays 

Fic. 3.—Restoration of Trissolepis kounoviensis; Permian, Bohemia. (After Fritsch.) 
features which were not long ago regarded as the essential characters of 
distinct groups; and the shape of the scales in future must only be 
cited among the minor diagnostic points of the old ‘ ganoid”’ fishes. 
We are acquainted with Jurassic fishes, indeed, in which the anterior 
scales are rhombic, ribbed, and united by peg-and-socket joints, 
