2 
II —DESCRIPTION OF THE GENERA AND SPECIES. 
A, From Dark Indurated Shale. 
Subclass — Elasmobraiichii. 
Order — ICHTHYOTOMX. 
Family — PLEURACANTHIDiE. 
Genus — PLEU RACANTHUS, Agassiz, 1837. 
(Poiss. Foss., iii, p. 66.) 
Gen. Char . — Teeth with thick depressed root, the crown consisting of 
two principal divergent cones, generally of unequal size, with a more or less 
minute intermediate denticle. A bilaterally-symmetrical spine, armed with 
two longitudinal series of recurved denticles, inserted at the back of the 
head. A single extended dorsal fin, separate from the dipliycercal caudal fin; 
two small anal fins. No shagreen or other dermal armour. 
Ohs . — This typically Upper Pakeozoic shark has not hitherto been 
found in the Southern Hemisphere. It occurs in the Carboniferous and 
Lower Permian of Europe, and in the Coal Measures of North America. 
Identical teeth have also been discovered in the Upper Trias (Keuper) of 
England. 
PLETJRACANTHUS PARVIDENS, sp. HOV. 
Plate I. 
Ohs . — The remains of this species are in a remarkable state of 
preservation, and the type specimen is the largest nearly complete skeleton 
of a Pleuracantk hitherto discovered. The most important examples for 
description are the following : — 
(a) Nearly complete fish, U43 m. in length, with traces of the dentition, 
hut with the spine only partly shown in impression ; to be regarded 
as the type specimen (PI. I, Pig. 1). 
