200 The True Sharks 
triangular scrrate teeth, very massive in substance, and without 
denticles. As only the teeth are known, the actual relations 
of the several species of Corax 
are not certainly known, and 
they may belong to the Lam- 
mide. 
Family Sphyrnide, or Ham- 
mer-head Sharks.—The S phyrnz- 
de, or hammer-headed sharks, 
are exactly like the Carcha- 
rud@ except that the sides of 
the head ‘are produced, so as 
to give it the shape of a ham- Fic. 142.—Teeth of Corax 
mer or of a kidney, the eye Pine ataee 
being on the produced outer edge. The species are few, but 
mostly widely distributed; rather large, voracious sharks with 
small sharp teeth. 
The true hammer-head, Sphyrna zygena, Fig. 143, is common 
from the Mediterranean to Cape Cod, California, Hawaii, and 
Japan. The singular form of its head is one of the most ex- 
traordinary modifications shown among fishes. The bonnet-head 
(Sphyrna tiburo) has the head kidney-shaped or crescent-shaped. 
It is a smaller fish, but much the same in distribution and habits. 
Intermediate forms occur, so that with all the actual differences 
we must place the Sphyrnide@ all in one genus. Fossil hammer- 
heads occur in the Miocene, but their teeth are scarcely different 
from those of Carcharias. Spliyrna prisca, described by Agassiz, 
is the primeval species. 
The Order of Tectospondyli—The sharks and rays having no 
anal fin and with the calcareous lamellae arranged in one or 
more rings around a central axis constitute a natural group to 
which, following Woodward, we may apply the name of Tecto- 
spondyli. The Cyclospondyli (Squalide, etc.) with one ring 
only of calcareous lamellae may be included in this order, as 
also the rays, which have tectospondylous vertebre and differ 
from the sharks as a group only in having the gill-openings 
relegated to the lower side by the expansion of the pectoral 
fins. The group of rays and Hasse’s order of Cyclospondyli we 
may consider each as a suborder of Tectospondyli. The origin 
