106 
DAVIS: NOTE ON CTILAMYDOSKLACHUS. 
edges round them, seem to be those of a young-, rather than an 
adult specimen. Compared with an Heptabranchias it agrees better 
with an emybro than an adult." The jaws are five inches in length, 
cartilaginous, somew^iat thick and twisted, and posteriorly are attached 
to a suspensorium connecting them w^ith the skull, which is three inches 
in length. The posterior surface of the suspensorium bears nine 
branchial rays. Tlie brain is small. In its outlines and proportions 
it shows great similarity to that of the Notidanidse, but it is 
comparatively much smaller than in the higher .sharks such as 
Carcharias or Zygcena. The olfactoiy and optic lobes and nerves are 
large as compared w'ith the whole of the brain. In the branchial 
cartilages the basi-branchials indicate a low rank in the developement 
of the fish. 
The vertebrae, for a short distance only behind the head, can be 
distinguished by constrictions, and are slightly calcified ; beyond, in 
the middle of the bod}^ the vertebra?- can only be distinguished by 
the apophyses. The notchchord is persistent. In the neural canal 
and between the interneurals llie segments are tolerably distinct. 
Over the abdominal cavity the haemal processes bear short flexible 
unseg-mented ribs. Above the anal fin the haemapophyses begin to 
take a downward blade-like extension, and are supplemented by 
small pieces of cartilag-e which further back become the radials of 
the caudal. The column ends abruptly ; the terminal segment 
resembles a slice taken from the front of a following vertebrae. 
The pectoral and ventral fins are supported by a well-defined 
cartilag-inous framework, attached to which are a series of three 
radials, the inner row elongate, the outer one short and small. A 
series of cartilages of irregular form support the dorsal and anal fins, 
they are disconnected from, or only connected by a membrane with, 
the vertebral apophyses. The cartilages of the dorsal fin are large 
as compared with the size of the fin itself, and appear to indicate 
that the fin in ancestral forms was much larger, and has become 
atrophied in the present specimen. 
The heart presents a somewhat peculiar form differing in details 
from the ordinary sharks. It has a small sub-quadangular ventricle, 
a large auricle, and a long bulbus arteriosus containing six rows of 
