GONIODONTS. 85 



direction transverse to that of the main tubes, and towards the 

 root. The main tubes terminate near the superficies of the tooth 

 in bold parallel curvatures. The greater part of the tooth of this 

 fish is surrounded by a thick and dense enamel, into many parts of 

 which the tubes of the dentine appear to be continued ; it is full of 

 fissures directed outwards. A kind of cement seems to surround the 

 base of the tooth." 



In his comparison of the structure of the enamel in the teeth of 

 different animals. Professor Retzius again refers to that of the Balistes, 

 and mentions the remarkable number and regularity of the fissures in 

 it, which, as he correctly states, somewhat resemble the tubes of the 

 dentine. " The csementum is characterized by its large, and extremely 

 irregular cells, which are in many parts confluent, or communicate im- 

 mediately, with each other. The minute plexiform tubes have an 

 extremely irregular course. This coating of cement is very thin, and 

 seems to terminate below the margin of the enamel. "(1) 



The similarity between the enamel and dentine of the file-fish, as 

 of the parrot-fish (see PL 50), is not less close in regard to the organ- 

 ization of their respective pulps, and their mode of calcification, 

 than in their microscopic structure when completely formed. The 

 ceementum is the result of the ossification of the capsule which 

 includes the pulps of the dentine and enamel ; and consequently it 

 corresponds in its coarse cellular structure with the rest of the 

 osseous system. 



GONIODONTS. (2) 



32. The teeth of all the species of this family are long, slender, 

 filiform, or setaceous, and are bent like awls or tenterhooks, whence is 

 derived the name of the family. In some of the genera, the teeth of 

 the short and broad intermaxillaries are disposed in lines radiating 

 from behind towards the anterior margin, and are thus somewhat ana- 

 logous to the vertical rows in which the teeth of the sharks are ar- 

 ranged. They further resemble the squaloid teeth in being attached, 

 not to the bone, but to the membrane investing the maxillse, and are 

 consequently moveable, both forwards and backwards. 



(1) Loc. cit. p. 541. (2) Ym-<.a, an angle, oisg, a tooth ; PI. 48, figs. 1, 2 and 3. 



