XVII ELASMOBRANCHII—PLAGIOSTOMI 443 
in one species (Votidanus cinereus), which exhibits a feeble 
asterospondylism in the caudal vertebrae. Skull amphistylie. 
Teeth unlike in the two jaws; those in the upper jaw usually 
with a large central cusp and smaller lateral cusps; those in the 
lower jaw comb-like, each consisting of numerous graduated 
pointed cusps inclining in the same direction, and supported on 
a long basal plate. 
The very few species included in this family are widely 
distributed in the tropical and subtropical regions of the Atlantic 
and Pacific Oceans. Notidanus (Heptanchus) cinereus, which has 
seven branchial arches and clefts, inhabits the Mediterranean 
and Atlantic. WV. (Hexanchus) griseus, with six branchial arches 
and clefts, has a similar distribution, but besides being an 
oceasional visitant to the British coasts, 1t is not uncommon at 
Cuba in the West Indies. It is said to grow to a length of 
26 feet. 
Fossil remains of Notidanus, principally teeth, occur in the 
Middle and Upper Jurassic, in the Cretaceous, and in the Eocene 
and Pliocene of England and the Continent. 
Fam. 2. Chlamydoselachidae (Frilled Sharks).—Body much 
elongate. Median fins as in Notidanus. Mouth nearly terminal. 
Nostrils lateral, nearly terminal, and without oro-nasal grooves. 
Branchial arches and clefts six. The outer margins of the inter- 
branchial septa are produced into overlapping cutaneous frills, 
the first of which is developed from the hyoid arch and overlaps 
the hyobranchial cleft, like a rudimentary operculum. Vertebral 
column as in the preceding family, but in the hinder part of the 
trunk the notochord is unconstricted and uniform in diameter, 
centra being absent. Skull hyostylic. Lateral line an open 
groove. ‘Teeth alike in both jaws, each consisting of a broad 
basal plate supporting three slender curved cusps, separated by a 
pair of much smaller cusps. 
The only living species known is Chlamydoselachus anguineus 
(Fig. 252),’ which occurs in the Pacific near Japan, in deep water 
off Madeira, and also off the Azores and the coast of Norway. 
It reaches a length of 4 to 5 feet. Teeth from the Pliocene 
deposits ‘of Tuscany have been referred to an extinct species, 
C. lawleyi. 
1 Garman, Bull. Mus. Comp. Zool. Harvard, xii. No. 1, 1885, p. 1; Giinther, 
Chall. Rep. Zool. xxii. 1887, p. 2. 
