26 BULLETIN OF THE 
mouth. Mouth anterior. Teeth with broad, backward-extended bases 
and slender cusps. Spiracles present. One dorsal, without a spine. 
An anal fin. Caudal without a pit at its root. The first gill-cover free 
across the isthmus. Intestine with a spiral valve. Anterior basibran- 
chial cartilages present. 
Chlamydoselachus. 
Six gill openings. Opercular flap, first gill-cover, broad. Teeth sim- 
ilar in both jaws; each with three slender, curved, subconical cusps, sep- 
arated by a pair of rudimentary denticles, on a broad base. No median 
upper series of teeth in front ; a series on the symphysis below. Mouth 
wide, without labial folds at the angles. Pupil horizontally elongate. 
Fins broad ; caudal without a notch. Basihyal elongate. The name is 
derived from xAapvs, a mantle, or frill, and céAaxos, a shark. 
The position of Chlamydoselachus in the system of recent sharks is 
not difficult to determine. Six gill-openings and the structure of the 
brain at once remove it from the others, and place the genus near the 
outlying genera Hexanchus and Heptabranchias. As it differs more 
than they do from other sharks, it lies farther from the main body of 
the Galei. The shape of the body, position of the mouth, articulations 
of the jaws, dentition, squamation, lateral line, pelvis, tail, and tropeic 
folds furnish characters sufficient to establish the distinctness of both 
genus and family. By such features as the chondrification, the unseg- 
mented notochord, the elongate bulbus, numerous cardiac valves, open 
lateral line, and the squamation, its rank is determined to be somewhat 
lower than that of the Notidanide. Possessing, as in the shagreen and 
certain cephalic peculiarities, more in common with Rhina (Squatina), 
though not at all closely related, it naturally falls into place in our lists 
between the latter and the mentioned family. 
What gives the new type a far greater importance than its standing 
among recent forms, however, is found in its affinities to some of the 
earliest known sharks, those of the Middle Devonian. Close affinity to 
the genus Cladodus makes it in present knowledge “the oldest living 
type of vertebrate.” 
In connection with its relationship to the early Selachia a number of 
perplexing questions present themselves for answer. Further accumula- 
tions of fossil material will be needed to determine how far success has 
attended the attempts here made to solve some of the problems. 
