186 The True Sharks 
younger than the Cestraciontes and little older than the Lam- 
noids, or the Squaloid groups. Heptranchias microdon is com- 
mon in English Cretaceous rocks, and Heptranchias primigenius 
and other species are found in the Eocene. 
Family Chlamydoselachide.—Very great interest is attached to 
the recent discovery by Samuel Garman of the frilled shark, 
Chlamydoselachus anguineus, the sole living representative of 
the Chlamydoselachida. 
Fig. 128.—Frill-shark, Chlamydoselachus anguineus Garman. From Misaki, 
Japan. (After Gunther.) 
This shark was first found on the coast of Japan, where it 
is rather common in deep water. It has since been taken off 
Madeira and off the coast of Norway. It is a long, slender, 
eel-shaped shark with six gill-openings and the palato-quadrate 
not articulated to the cranium. The notochord is mainly 
persistent, in part replaced by feeble cyclospondylic vertebral 
centra. Each gill-opening is bordered by a broad frill of skin. 
There is but one dorsal fin. The teeth closely resemble those 
of Dittodus or Didymodus and other extinct Ichthyotomt. The 
teeth have broad, backwardly extended bases overlapping, 
the crown consisting of three slender curved cusps, separated 
by rudimentary denticles. Teeth of a fossil species, Chlamy- 
doselachus lawleyt, are recorded by J. W. Davis from the Pliocene 
of Tuscany. 
Order Asterospondylii—The order of Asterospondylt comprises 
the typical sharks, those in which the individual vertebra are 
well developed, the calcareous lamelle arranged so as to radiate, 
star-fashion, from the central axis. All these sharks possess 
two dorsal fins and one anal fin, the pectoral fin is normally 
