DENTAL SYSTKJI OF FISHES. 221 



the Wrasse i^Labriis, V, pi. A5.Jig. 4.). Sometimes the hemispheric 

 teeth are so numerous, and spread over so broad a surface, as to 

 resemble a pavement {Chrysophi'ys, V, pi. 45. Jigs. 3. 6 ; and Pisodus, 

 pi. Al.fig. 3.) ; or they may be so small, as well as numerous {denies 

 graniformes), as to give a granulated surface to the part of the 

 mouth to which they are attached (premaxillaries of Labriis, V, 

 pi. 45. ,y?^. 1.). A pi'ogressive increase of the transverse over the 

 vertical diameter may be traced in the molar teeth of diflferent fishes, 

 and sometimes in those of the same individual, as in Labrus (V, pi. 45. 

 fig. 4) and Placodus (V, pi. 30.), until the cylindi'ical form is exchanged 

 for that of the depressed plate. vSuch dental plates {denies lamelli- 

 formes) may be found, not only circular, but elliptical, oval, semilunar, 

 sigmoid, oblong, and even, as above-mentioned, square, hexagonal, 

 pentagonal, or triangular ; and the grinding surface presents as 

 various and beautiful kinds of sculpturing. The broadest and thinnest 

 lamelliform teeth are those that form the complex grinding tubercle of 

 the Diodon (V, pL SS-^tv/. 2.). The front teeth of the Flounder and 

 Sargus present the form of compressed plates, at least in the crown, 

 and are true ' denies incisiviJ Numerous wedge-shaped dental plates 

 {denies cuneaii) are set vertically in the pharyngeal bones of the 

 Parrot-fish {Scams, V, pi. 51.). A thin lamella, slightly curved like 

 a finger-nail, is the singular form of tooth in an extinct genus of fishes, 

 which I have thence called Petalodus (V, pi. 22. figs. 3, 4, 5.) 

 Sometimes the incisive form of tooth is notched in the middle of the 

 cutting edge, as in Sargus tinimaculaius (V, pi. I. fig. 9.). Sometimes 

 the edge of the crown is trilobate {Aplodacti/lus, ib.fig. 10.). Some- 

 times it is made quinquelobate by a double notch on each side of the 

 large middle lobe {Boojis, ib.fig. 11.). In the formidable Sea-pike 

 {Sphyrcena Barracuda, V, pi. 53.) the crown of each tooth, large and 

 small, is produced into a compressed and sharp point, and resembles a 

 lancet. Sometimes the edges of such lancet-shaped teeth are finely 

 serrated, as in Priodon (V, pi. \. fig. 12.), and the great Sharks of the 

 genus Carcharias, the fossil teeth of which indicate a species {Carch. 

 Megalodoti) sixty or seventy feet in length. 



The lancet is changed for the stronger spear-shaped tooth in the 

 Sharks of the genus iMmna, and in the allied great extinct Otodus, 

 as in the small Porbeagle, similarly shaped, but stronger, jjiercin"- 

 and cutting teeth were accompanied by one or more accessory com- 

 pressed cusps on each side their base, like the Malay crease. 



With respect to situation, the teeth, in Sharks and Rays, are limited 

 to the bones (maxillary and mandibular), which form the anterior 

 aperture of the mouth : in the Carp and other Cyprinoids the teeth 

 are confined to the bones which circumscribe the posterior aperture 

 of the mouth, viz. the pharyngeals and basi-occipital. The Wrasses 



