SHARKS. 29 



the destructive character of its maxillary armour. The characteristic 

 dentition of the shark tribe may be studied with advantage in the 

 spotted and spiny dog-fishes common on our coasts ; the former, 

 which is the type of the genus Scyllium, exhibits teeth of a triangular 

 form with a large middle cusp, complicated, at least, in the young 

 animal, with one or two small cusps on each side of its base ; the 

 base is always more or less furrowed longitudinally. In Crossorhinus, 

 a sub-genus of Scyllium, the teeth are characterized by having the 

 osseous base divided into three lobes. In Ginglimostoma, the teeth have 

 a simple rhomboidal base supporting one large median cone, and from 

 two to four obtuse denticles on each side : the teeth of this genus of 

 dog-fish are remarkable for their somewhat unusual number, there 

 being frequently ten in each vertical row. 



In the spiny or piked do^-fish fSpinax, Cuv.), the teeth (PI. 3, 

 fig. 3,) are alike in both upper and lower jaws ; they are thin trian- 

 gular plates with the apex inclined backwards, so that the anterior 

 edges are opposed to each other ; the enamel does not terminate 

 below in a horizontal line, but is continued along the middle of the 

 bony base. In an allied species, the teeth of the upper jaw are 

 smaller and of a different form from those of the lower jaw, being tri- 

 cuspid, as in the spotted dog-fish ; some ichthyologists restrict the 

 subgeneric name Spinax to the spiny dog-fishes which are cha- 

 racterized by this modification of the teeth. 



In the genus Notidanus, the teeth are not only of diff'erent forms in 

 the upper and lower jaws, but also vary considerably, in this respect, 

 at the anterior and posterior regions of the same jaw, (PL 3.) 

 In the upper jaw, the anterior teeth are large, compressed, triangular 

 plates, with the pointed apex arched backwards, and the margins 

 slightly dentated, except in the two anterior ones. The posterior 

 teeth are in the form of simple obtuse furrowed tubercles. In the 

 lower jaw, the large anterior teeth have the apex less produced ; the 

 anterior margin is finely serrate, and the posterior divided into three 

 or more denticles. The posterior minute teeth resemble those in the 

 upper jaw. Of the larger teeth there are rarely more than four in 

 each vertical row. 



In the subgenus Carcharias, the teeth present the form of 



