PISCES. 
65 
lip, until this phenomenon culminated in the strange spiral 
known as Helicoprion (Fig. 62) from the Permo-Carboni¬ 
ferous of Eussia, Japan, and Australia (Table-case 2). 
Fig. 62.—Spiral row of teeth of Helicoprion bessonowi , from the Permo- 
Carboniferous of Perm, Russia; one-quarter nat. size. a. new teeth 
being formed; b. teeth in use; c. old teeth passed out of use. (After 
A. Karpinsky. Table-case 2.) 
Edestus is a nearly similar cluster of teeth from the Car¬ 
boniferous of North America and Europe. The sharks to 
which these teeth belonged may have been Pleuropterygii, 
but their relationships are still uncertain. 
Order III.— ICHTHYOTOMI. 
These are sharks with the paired fins paddle-shaped and 
supported by a more or less branched arrangement of 
cartilages like that in the paddles of Dipnoan fishes and 
Crossopterygii (p. 81). Pleuracanthus (Fig. 63) is the 
typical genus, represented in Table-case 2 by nearly complete 
fishes from the Lower Permian of Germany and Bohemia, 
and by spines and teeth ( Diplodus ) from various European 
and American Carboniferous and Lower Permian rocks. 
F 
Table-ease 
2 . 
Table-case 
2 . 
