generalized genera, they vary from 1 to about 10 in num- 

 ber. The teeth of the upper and lower jaws are basically 

 similar, but there are usually a few more teeth in the 

 lower jaw than in the upper. In a few moderately to 

 highly specialized genera the teeth are truncate rather 

 than conical, while the fossil genera sometimes have en- 

 larged teeth. 



In triacanthids there is an outer series of about 8 to 10 

 heavy incisors in each jaw, internal to which are several 

 more or less molariform teeth, usually 4 (2 in one genus) 

 in the upper jaw and 2 in the lower. The structure and 

 number of the teeth in balistids are strikingly similar to 

 those found in triacanthids, for in balistids the heavy in- 

 cisors invariably (with rare individual exceptions) occur 

 in an outer series of eight teeth and an inner series of six 

 teeth in the upper jaw, while in the lower jaw there is 

 only a single series (corresponding to the outer series of 

 the upper jaw) of eight teeth. The number of teeth 

 becomes further reduced in monacanthids to six in an 

 outer series in the upper jaw and six (sometimes only 

 four) in the outer series of the lower jaw, with an inner 

 series of four teeth in the upper jaw and no inner series 

 teeth in the lower jaw. 



The dental formulae of the various balistoids have 

 been common features of the diagnoses of that group ever 

 since the time of Bleeker ( 1866:8- 10) , who was the first to 

 give prominent attention to these differences. The 

 development of balistoid teeth from deep sockets in con- 

 tinuity with the pulp cavity was accurately described for 

 the first time by Owen (1840 & 1845:82-85). Goodrich 

 ( 1909:438, fig. 448) gave a figure of the replacement teeth 

 developing in Balistes, and Isokawa (1955) presented a 

 description of the general development and histology of 

 the teeth in monacanthids. The teeth of ostracioids are 

 elongate and rodlike, with between 6 and 17 teeth in a 

 single series in each jaw. 



The teeth of gymnodonts are so highly modified that 

 they have attracted a great deal of attention in the 

 literature. There is, however, a phyletically important 

 distinction to be made about the teeth of the various 

 gymnodont subgroups which usually is not clearly 

 stated. In Triodon and diodontids the teeth always take 

 the form of relatively small £uid discrete units which 

 become densely packed with one another and incor- 

 porated with the bony matrix of the premaxillary and 

 dentary. In tetraodontids the teeth are relatively more 

 discrete long rods which lie parallel to the biting edge of 

 the jaws. There are no discrete teeth present in the jaws 

 of molids, nor can any individual tooth primordia be 

 found in the pulp cavity. The intimate incorporation of 

 the teeth with the bony matrix of the premaxillary and 

 dentary has reached its zenith in the molids, and one can 

 only speculate that the highly irregular surface of the 

 floor of the pulp cavity, with its numerous individual 

 "tooth" or bone forming cavities, indicates that the 

 molid condition has evolved from the Triodon and 

 diodontid type rather than from the tetraodontid type. 



The structure, and even the mere presence or absence, 

 of a trituration plate is also of diagnostic interest. In 

 Triodon a trituration plate composed of right and left 



halves is present in the upper jaw, while the trituration 

 plate of the lower jaw is undivided. In both jaws about 

 five individual teeth can be seen at the posterior edge of 

 the trituration plate to each side of the midline. In 

 diodontids and molids there is a trituration plate in each 

 jaw, but the number of dental units that go into its make 

 up differs. In diodontids there is a single dental unit 

 along the posterior edge of each half of the trituration 

 plate in each jaw, except for one species with several den- 

 tal units. In molids there is a single dental unit along the 

 posterior edge (and sometimes anteriorly) of each half of 

 the trituration plate in the upper jaw, but in the lower 

 jaw several such teeth are present. 



Steenstrup and Lutken (1898) described the dif- 

 ferences between the trituration plates in two genera 

 {Mola and Rumania) of molids, as did Hilgendorf (1893). 

 Wahlgren (1867) gave one of the earliest and best de- 

 scriptions of the trituration plate in Mola, and his figure 

 of that structure was reproduced by Steenstrup and Lut- 

 ken. Trituration plates are never developed in canthigas- 

 terins, but, contrary to Fraser-Brunner (1943), they are 

 sometimes present in tetraodontins. In the upper jaw of 

 many tetraodontids there is a single longitudinal series of 

 a small number of teeth, to each side of the midline. In 

 the lower jaw, however, these trituration teeth are of less 

 frequent occurrence. They have been reported in the 

 lower jaws of several tetraodontids by Kaschkaroff 

 (1914a:317-318), in the lower jaw of the tetraodontid 

 Colomesus by Pinto (1959), and in many other tetra- 

 odontids described here. There are a number of papers 

 describing the general structure of the teeth in plectog- 

 naths to which the reader should be referred before 

 passing on to other topics. Cuvier (1805, vol. 3) gave de- 

 scriptions of the gross morphology of the teeth in plectog- 

 naths, but it was not until Owen (1840 & 1845) that their 

 detailed structure was made known. Owen took excep- 

 tion to the view advocated by Cuvier (1805, 3:125) and by 

 Bom (1827) that the dental lamellae in gymnodonts 

 develop by the "apposition or the transudation of layers 

 of calcareous matter from the pulp's surface" (Owen 

 1840:77). On the contrary, Owen showed that these 

 lamellae developed by "intus-susception or the deposi- 

 tion of calcareous tubes in the pulp's substance." Owen 

 pointed out that whereas the teeth of the biting part of 

 the jaws in diodontids and tetraodontoids were dif- 

 ferent, there was a marked similarity between the dental 

 lamellae of the trituration plate of diodontids and the 

 elongate dental lamellae of the biting portion of the jaws 

 in tetraodontids. A more modem treatment of the 

 general anatomy of the teeth in gymnodonts is that 

 presented by Pflugfelder (1930), Andreucci (1966a, b, 

 1967a, b, 1968a, b, 1969, 1970), Andreucci and Britski 

 (1968a, b, 1969a, b, 1970, 1971), and Andreucci and 

 Blumen (1971). The rodlike structure of the dental units 

 of tetraodontids and the platelike trituration lamellae 

 have been described by a number of workers other than 

 those mentioned above, notably by Goodrich (1909), 

 Ghigi (1921), and Tretjakoff (1926c). Jenyns (1842:150) 

 was probably the first to call attention to the discrete 

 dental units that are visible on the external surface of the 



