FORM 



laniary or canine teeth of the carnivorous quadrupeds. Of this kind 

 are the larger teeth of the pike and Rhizodus (PI. 35), and the 

 anterior teeth of the Dentex, (PL 41). A moderately long, stout 

 and more or less straight cone is a form exemplified in the anterior 

 teeth of the wolf-fish, (PI. 60 & 61 ,) and the transition by progressive 

 blunting, flattening and expansion of the apex is very gradual from 

 this form of the cone to the thick and short cylinder, such as is seen 

 in the posterior teeth of the wolf-fish, and similar grinding or 

 crushing teeth of many other existing genera. The working surface 

 of these short cylindrical teeth may be rounded as in the sheep's- 

 head-fish {Sargus, PL 42, fig. 1,) or flattened as in the pharyngeal 

 teeth of the wrasse, {Labrus, PI. 45, fig. 4). Sometimes the hemi- 

 spheric teeth are so minute and numerous as to give a granulated 

 surface to the part of the jaw to which they are attached (PL 45, fig. 1). 



A progressive increase of the transverse over the vertical dia- 

 meter may be traced in the molar teeth of different fishes, and 

 sometimes in those of the same individual, until the cylindrical form 

 is lost in that of the depressed plate. Of this change we have a good 

 example in the posterior teeth of the gilt-head {Chrysophrys) , when 

 arrived at maturity, and likewise in the fossil genus Placodus^ 

 (PL 30). The dental plate, instead of offering the cylindrical form, 

 may be elliptical, oblong, square, triangular, semilunar, sigmoid, 

 and with the grinding surface variously sculptured. The broadest 

 and thinnest depressed laminae are seen in the component denticles 

 of the molar tubercle of the diodon, and in the teeth of the Phyllodus. 



The incisors of the sargus, (PL 1, fig. 13,) flounder, and some 

 other fishes present the compressed laminated form, at least, in the 

 protruded coronal portion. Numerous wedge-shaped dental plates 

 are set vertically in the pharyngeal bones of the Scarus or parrot- 

 fish. A thin lamella, slightly concave like a finger-nail, is the sin- 

 gular form of the tooth of an extinct genus of cartilaginous fishes, 

 which I have, on that account, ndnned Petalodus, (PL 22, figs. 2, 3, 4.) 

 Sometimes the flattened incisive crown is notched in the middle of 

 the cutting edge, as in the incisors of the species of bream {Sargus 

 unimaculatus) figured in PL 1, fig. 9. Sometimes there is a double 

 notch rendering the crown of the incisor trilobate, as in the genu§ 



B 2 



