Animal Dentition 255 
of two large lateral cones with a much smaller cone between them; and they were 
implanted by broad bases in such a manner that they interlocked with their fellows 
of the opposite jaw, and thus teeth of several longitudinal series were in use at the 
same time. The modern form of shark-dentition—whether of the piercing or crushing 
type—in which not more than one or two series are in use simultaneously, has been 
brought about by the deepening and narrowing of the base of attachment of the 
individual teeth, rendering their support less fixed, and not permitting them to come 
into use until they attain the summit or pass to the outer side of the jaw-cartilage. 
The complete dental apparatus of ordinary Sharp-Toothed Sharks is so well known 
that it has been thought unnecessary to give a figure, and the cuts are therefore 
devoted to the illustration of a few of the more distinctive types of individual teeth 
in this group. The simplest type of tooth is presented by the Porbeagle Shark and its 
immediate relatives. The crowns of such teeth are formed by a single dagger-like cone, 
frequently flanked on each side of the base by one or more small denticules. The 
cutting-edges of such teeth are deyoid of serrations. The compressed form of the 
base characteristic of all modern sharks is well shown in Fig. 4. From such a 
type of tooth there is a gradual transition to one in which the “dagger” becomes 
very much shorter and broader, with its cutting-edges broken up into fine serrations. 
In the existing Rondelleti’s White Shark, which has teeth of this type and attains 
a length of about forty feet, the bases of the individual teeth measure a little short 
of a couple of ches. What, then, must have Gia h 
been the dimensions of the species to which Gee ” Gian aR > 
teeth lke the one represented in Fig. 4 per- sain Be Th LAU] 
tamed, some of such teeth having a_ basal Fish hah 
length of fully four inches? ‘Teeth of this eon Qe? IN 
type have been dredged from the ooze of the  fyiyyu A nd PS 
8 HO gd 
bed of the Pacific in such a condition as to 
indicate that the monsters to which they 
belonged lived, probably, at no VERY great Fig. 6. Two Crushing-Teeth of the extinct Carboniferous 
time ago. Shark Orodus. From the Mountain Limestone of 
By the imerease in number and size of the pa 
lateral denticules found at the two basal edges of so many sharks’ teeth, accompanied 
by a proportionate diminution of the central ‘dagger,’ may have been evolved the 
very remarkable type of tooth (Fig. 5) characteristic of the Comb-Toothed Sharks. 
Six or seven transverse rows of such formidable teeth (of which, by the way, the 
upper are somewhat more simple than the lower ones) ave developed in each jaw, and, 
unlike other modern sharks, several longitudinal rows of these are in use at the 
same time. 
Allied in several respects to the comb-toothed sharks, more especially by this 
simultaneous use of several longitudinal series of teeth, are the Pavement-Toothed or 
Port Jackson Sharks, the sole survivors of a once dominant group, many of the members 
of which attained dimensions far exceeding those of their modern relatives. The teeth 
of these sharks, as shown in the jaw represented in Vig. 2, differ from those of any 
of the species hitherto considered in the assumption of a flattened, pavement-like form 
by those in the hinder part of the series. The largest of these pavement-like teeth 
are those of the sixth transverse row from the hinder end. It will be noticed that 
all these teeth have a finely-granular surface, except on a very narrow mouth-hke 
ridge running along the summit of the crown, this ridge representing the last vestige 
of the “dagger” of an ordinary shark’s tooth. From the large sixth row there is a 
eradual diminution in the size of the teeth as we pass forwards, accompanied, as the 
extremity of the jaw is approached, by a greater development of the central midge of 
