FORM. SITUATION. 



Aplodactylus, (fig. 10) ; in the lower maxillary teeth of the Boops, 

 the crown is divided into five lobes by a double notch on each side 

 of the middle and largest lobe, (fig. 11), 



In the great barracuda-pike (Sphyroena) , the crown of both the 

 large and small lamelliform teeth is produced into a sharp point, and 

 closely resembles a lancet, (PL 1, fig. 4, & PI. 53). A similarly 

 shaped piercing and cutting tooth may be accompanied by one or 

 more accessory compressed cusps at its base, as in the teeth of cer- 

 tain sharks, (PL 3 & 4,) or the margins of the crown may be variously 

 notched, serrate, e. g., as in the priodon, (PL 1, fig. 12,) and in the 

 teeth of the great sharks of the genus Carcharias, or crenate as in the 

 genus, hence called Crenidens, (fig. 7,) and in the teeth of the Acan- 

 thuri, (PL 44,) of which the species called Ctenodon is remarkable for 

 the deeply crenated, expanded and spatulate crowns of its teeth, (PL 

 1, fig. 6). Prismatic teeth of three sides are present in the jaws 

 of the Myletes, where each angle of the coronal surface is produced 

 into a point. The small teeth with which the jaws of the Scarus are 

 paved are four sided prisms ; the strong flat teeth which form the 

 tesselated pavement of the jaws of the Eagle-rays {Myliobates), present 

 beautifully regular hexagonal or pentagonal forms (PL 25). 



4. Situation. — Before proceeding to consider the situation of 

 the teeth of fishes, a few words may be premised respecting the 

 bones which enter into the formation of the mouth in the ordinary 

 osseous species. In these, the upper margin of the mouth is 

 bounded generally by the intermaxillary bones alone, which extend 

 backwards from the middle line to the angles of the mouth ; in 

 this case, the superior maxillary bones (1) run parallel with and above 

 the horizontal portion of the intermaxillaries ;(2) but when, as in 

 the lophius and salmon-tribe, the intermaxillary bones do not 

 extend to the angles of the mouth, the osseous boundary is com- 

 pleted above by the superior maxillaries.(3) The lower border of 

 the mouth is formed by the premandibular bones, (4) this name being 

 given to the anterior of the two pieces of which each ramus of 

 the lower jaw consists in fishes. The roof of the mouth is formed 

 anteriorly by three bones which extend backwards from the inter- 

 space of the intermaxillary bones ; the two lateral ones are the pa- 



(1) PI. 41, b. (2) PI. 41, a. (3) PI. 60, fig. 1, b. (4) PI. 41, c. 



