88 PRIMITIVE LIVING SHARKS 
Recent Sharks 
The fornis of Sharks and Rays 
common at the present time are 
generally looked upon as closely 
related genetically, although 
their lineage cannot be defi- 
nitely traced. As far as pale- 
ontological evidence goes, they 
may well have been derived 
from a single Palzozoic an- 
vestor. . 
Perhaps of all recent forms, 
Chlamydoselache (Fig. 92), and 
Notidanus (Heptanchus, or Hep- 
tabranchias) (Fig. 93), which are 
universally regarded as. “ primi- 
tive,’ have inherited most di- 
rectly the features of this gen- 
eralized Paleozoic form. But 
which of these two sharks must 
be regarded as resembling its re- 
mote ancestor the more closely 
seems to the writer a very doubt- 
ful matter. Chlamydoselache 
derives its great interest from 
its late discovery (1884, Gar- 
man), rareness, and Pleuracan- 
thid type of teeth. (Fig. 92, A) ; 
but now that it has been taken 
in numbers — comparatively — 
in deep water, one is inclined 
to believe that many of its 
Fig. 93.— Heptanchus, Heptabranchias maculatus. 2. X 4, From specimen loaned by Smithsonian Institution. Collected 
in Pacific, 
N’, NW”. Anterior and posterior nares. SP. Spiracle. 
