sal spine. How constant this pair of nubbins are in their 

 occurrence cannot be determined until more specimens 

 of this species are available for clearing and staining, but 

 I suspect that the nubbins represent the right and left 

 basal regions of a rudimentary spine. In all other plec- 

 tognaths with two or more dorsal spines, the first two 

 spines are always borne on the first basal pterygiophore, 

 while the spines posterior to them are each borne on in- 

 dividual basal pterygiophores, which additionally leads 

 me to believe that the paired nubbins in T. macropterus 

 are homologous to the first dorsal spine in other plec- 

 tognaths and that the two relatively well -developed 

 spines in T. macropterus are homologous to the second 

 and third spines of other plectognaths. U that is true, 

 Triodon exhibits a feature not seen in other plectog- 

 naths with a spiny dorsal fin, for when the size and 

 number of the dorsal spines decreases in the 

 triacanthoids and balistoids it is always by reduction and 

 loss of elements from posteriorly to anteriorly in the 

 series, and the first spine is always much larger than the 

 others. 



Two other bony elements without intemeural processes 

 are placed above the dorsal ends of the neural spines be- 

 tween, and in series with, the two basal pterygiophores 

 supporting the dorsal spines and the first basal pterygio- 

 phore of the soft dorsal fin. When a spiny dorsal fin is not 

 present, these four elements anterior to the anterodorsal 

 end of the first basal pterygiophore of the soft dorsal fin 

 would be called supraneurals. But where the two more 

 anterior elements in the series support dorsal spines, 

 they must be referred to as basal pterygiophores, even 

 while the two more posterior elements technically remain 

 supraneurals. Thus, the distinction between supra- 

 neurals and basal pterygiophores in Triodon is ar- 

 bitrary, and indicates that the supraneural element that 

 occurs in ostracioids and gymnodonts is probably a 

 simplified basal pterygiophore that no longer supports 

 dorsal fin spines. 



Of the four elements that are supraneural in position 

 in Triodon, the first (the first basal pterygiophore when a 

 spiny dorsal fin is present) is by far the largest and ar- 

 ticulates by fibrous tissue anteriorly with the distal end 

 of the neural spine of the fourth abdominal vertebra, 

 ventrally with the distal ends of the neural spines of the 

 fifth and sixth abdominal vertebrae, and posteriorly with 

 the anterior edge of the second element. The second ele- 

 ment is much shorter than the first and articulates by fi- 

 brous tissue anteriorly with the first, ventrally with the 

 neural spine of the seventh abdominal vertebra and pos- 

 teriorly with the anterior edge of the third element. The 

 third element is slightly shorter than the second and ar- 

 ticulates anteriorly by fibrous tissue with the second and 

 with the neural spine of the seventh abdominal verte- 

 bra. Posteriorly the third element slightly interdigitates 

 with the anterior edge of the fourth, while posteroven- 

 trally it articulates by fibrous tissue with the first basal 

 pterygiophore of the soft dorsal fin. The small fourth ele- 

 ment articulates by interdigitation ventrally with the 

 first basal pterygiophore of the soft dorsal fin and an- 

 teriorly with the third element. 



Fin rays and ptery^ophores. — Eleven fin rays pres- 

 ent; the first ray unbranched, the others branched in 

 single, double, or triple dichotomies; third and fourth 

 rays longest; first ray about equal in length to the next to 

 last ray. Each fin ray has a well-developed pair of distal 

 pterygiophores as two distinct halves between the bifur- 

 cate base of the ray. In the smaller specimen the two 

 halves are not in close contact with one another, while in 

 the larger specimen the two halves have their medial 

 edges in close apposition and are held firmly together by 

 fibrous tissue and in some cases apparently by slight in- 

 terdigitation. The fin rays are supported basally through 

 fibrous tissue by ii basal pterygiophores, which ar- 

 ticulate with one another and with the neural spines of 

 the vertebrae by fibrous tissue. The dorsal ends of the 

 basal pterygiophores are slightly enlarged and are in 

 close contact with one another. The upper lateral sur- 

 faces of the first three or four basal pterygiophores 

 possess shallow lateral flanges, but these flanges de- 

 crease in size posteriorly in the series and are effectively 

 absent on the last few pterygiophores. The pterygio- 

 phores are cartilage filled at both ends. The intemeural 

 portions of the pterygiophores articulate between the 

 neural spines of the seventh abdominal to the fourth 

 caudal vertebrae. 



Anal Fin. 



Fin rays and pterygiophores. — Ten fin rays pres- 

 ent; the first ray unbranched, the others branched in 

 single, double, or triple dichotomies; third and fourth 

 rays longest; first ray about as long as the last ray. Each 

 fin ray has a well-developed pair of distal pterygiophores 

 as two distinct halves between the bifurcate base of the 

 ray, with the two halves in close apposition medially only 

 in the larger specimen, just as with the soft dorsal fin. 

 The fin rays are supported basally through fibrous tissue 

 by nine basal pterygiophores, which are cartilage filled at 

 both ends. At their distal ends the pterygiophores are 

 slightly expanded anteroposteriorly, but they do not 

 make as close a fibrous tissue contact with one another as 

 do the soft dorsal fin basal pterygiophores. Other than at 

 their distal ends, the anal fin pterygiophores, with the 

 exception of the first, are slender shafts without any 

 lateral projections or flanges from their surfaces. The 

 first pterygiophore is a much stouter shaft and ventrally 

 it possesses a large lateral flange to either side of its an- 

 terior edge. The second pterygiophore is extremely thin, 

 and is held between the first and third pterygiophores 

 without reaching dorsally to make contact with a haemal 

 spine. The other pterygiophores articulate by fibrous tis- 

 sue dorsally with the haemal spines of the first to fifth 

 caudal vertebrae. 



Anatomical diversity.— The single Recent species of 

 this family apparently consists of two at least partially 

 reproductively isolated populations (Tyler 1967) differ- 

 ing grossly only in that the population from Japan to In- 

 donesia usually retains a rudimentary spiny dorsal fin 



254 



