Fig. 117.—Confluent nasal and buccal cavities of the same fish.
Crossorhinus.—The first dorsal behind the ventrals, the second in advance of the anal, which is very close to the caudal. Tail rather short. Eyes small. Spiracle a wide oblique slit, behind and below the eye. Nasal and buccal cavities confluent. Head broad, flat, with the snout very obtuse; mouth wide, nearly anterior. A free nasal cirrhus; sides of the head with skinny appendages. Anterior teeth rather large, long and slender, without lateral lobes, the lateral tricuspid, smaller, forming a few series only. The fourth and fifth gill-openings close together.
Three species are known from the Australian and Japanese coasts. They are evidently ground-sharks, which lie concealed on the bottom watching for their prey. In accordance with this habit their colour closely assimilates that of a rock or stone covered with short vegetable and coralline growth—a resemblance increased by the frond-like tentacles on the side of the head. This peculiarity of the integuments, which is developed in a yet higher degree in Pediculati and Lophobranchs, is not met with in any other Selachian. These Sharks grow to a length of 10 feet.
Sixth Family—Hybodontidæ.
Two dorsal fins, each with a serrated spine. Teeth rounded, longitudinally striated, with one larger, and from two to four smaller lateral cusps. Skin covered with shagreen.
Extinct. From carboniferous, liassic, and triassic formations. Several genera have been distinguished; and if Cladodus belongs to this family, it would have been represented even in the Devonian.
Fig. 118.—Spine of Hybodus subcarinatus.