THE COMB-TOOTHED SHARKS 



2907 



with a slight longitudinal ridge and a net-like ornamentation. The spines of the 

 dorsal fins are smooth, covered on the sides with a thick layer of ganoine; the 

 shagreen is fine; and the head is devoid of spines. In the existing species the egg 

 capsules assume a remarkable 

 screw-like form, quite unlike 

 that of any other member of 

 the family. The living mem- 

 bers of the genus, none of 

 which exceed five feet in 

 length, have been recorded 

 from the seas of Japan, Am- 

 boyna, Australia, the Galapa- 

 gos Islands, and California; 

 while remains of extinct 

 forms occur in the Cretaceous 

 and Upper Jurassic strata of 

 Europe. Very little appears 

 to be known as to their 

 habits; but their food is stated 

 to consist principally of mol- 

 lusks, the hard shells of which 

 are crushed by the pavement- 

 like hinder teeth. 



Of the numerous fossil genera of the family only a very brief men- 

 ypes tion can be made. One of the earliest is the Carboniferous Orodus, 

 with teeth very like those of the later Hybodus, ranging from the Trias to the lower 

 Cretaceous. In the last-named genus the notochord is persistent, the bluntly 

 conical or cusped teeth have a central and two or more lateral cusps, the fin spines 

 are ridged, and there are two hook-like spines below each eye. Acrodus, with a 

 nearly similar range, has on the other hand, blunt teeth; while the Jurassic Aster- 

 acanthus differs from Hybodus by its rhomboidal, roughened, and flattened teeth, 

 and the star-like ornamentation of the spines of the dorsal fins. In Synechodus 

 of the Chalk all the teeth are cusped; the anterior ones having a tall central cusp, 

 flanked with from three to five small lateral pairs. An allied extinct family 

 {Cochliodontida) i confined to the Carboniferous rocks, differs by the component 

 teeth of at least one of the oblique rows being fused into a continuous curved plate, 

 which may be either smooth or ridged. Many of the extinct representatives of 

 these families exceeded the Port Jackson shark in size. 



I,OWER JAW OF PORT JACKSON SHARK. 

 (One-half natural size.) 



THE COMB-TOOTHED SHARKS Family NOTIDANIDsE 



A very remarkable family is now represented by the four species of comb- 

 toothed sharks (Notidanus} and the frill-gilled shark (Chlamydoselache anguineus), 

 the latter of which is shown in the illustration. Whereas in all other sharks the 



