the fin rays are supported by about 14 basal pterygia- 

 phores, which decrease in size posteriorly in the series. 

 The more anterior of the pterygiophores have weakly 

 developed lateral flanges along their lengths, but these 

 lateral projections for muscle attachment become reduc- 

 ed posteriorly in the series and are entirely absent from 

 the more posterior pterygiophores. The basal pterygio- 

 phores articulate by fibrous tissue ventrally with the 

 neural spines of the vertebrae. The first and second basal 

 pterygiophores of the soft dorsal fin are usually located 

 between the neural spines of the eighth abdominal and 

 first caudal vertebrae while the last basal pterygiophore 

 is located between those of the sixth and seventh caudal 

 vertebrae. The basal pterygial elements are cartilage fill- 

 ed at their dorsal and ventral ends. 



Anal Fin. 



Fin rays and pterygiophores. — Fourteen fin rays 

 usually present; the first ray and the last ray un- 

 branched, the others branched in single or double 

 dichotomies. Each fin ray has a small pair of distal 

 pterygiophores as two distinct halves between the bifur- 

 cate base of the ray, except for the last one or two rays, in 

 which these elements, if present, are unossified. Basally 

 the fin rays are supported by about 13 basal pterygio- 

 phores, which decrease in size posteriorly in the series. 

 They possess weakly developed lateral flanges for muscle 

 attachment along their lengths, as in the case of the dor- 

 sal fin basal pterygiophores, and they are cartilage filled 

 at their dorsal and ventral ends. The first basal pterygio- 

 phore is by far the largest of the series and has well- 

 developed lateral flanges for muscle attachment along 

 each side of its anterior surface. It articulates by fibrous 

 tissue to the posterior surface of the bifid portion of the 

 haemal spine of the first caudal vertebra and to the 

 anterior surface of the haemal spine of the second caudal 

 vertebra. The 2d to 13th basal pterygiophores articulate 

 by fibrous tissue to the haemal spines of the 2d to 7th 

 caudal vertebrae. 



pelvic fin, if it is present at all. Two species: Protobalis- 

 tum imperiale (Massalongo 1857) and Spinacanthus 

 cuneiformis (Blainville 1818). 



The Eocene Eoplectinae differ from both the 

 Spinacanthinae and the Recent species in having: 

 gymnodontlike jaws and upper jaw suspension, with 

 numerous small rounded dental units incorporated in the 

 matrix of the premaxillary and dentary, with the 

 premaxillary and maxillary immovably articulated, and 

 the jaws probably nonprotrusible; a well-developed 

 pelvic fin of one spine and four long branched rays; the 

 ventral shaft of the second basal pterygiophore of the 

 spiny dorsal fin directed anteroventrally and articulated 

 either to the base of the skull or between the neural 

 spines of the first and second vertebrae; 9 4-11 vertebrae 

 in a highly arched column; decidedly more soft dorsal 

 and anal fin rays than basal pterygiophores. Two 

 species: Eoplectus bloti Tyler (1973b) and 

 Zignoichthys oblongus (Zigno 1874a). 



The Recent species are divided into two subfamilies 

 mainly on the basis of the shape of the posterior portion 

 of the skull, the placement of the epiotics and the shape 

 of the pelvis, none of which features are known for the 

 fossil species. Comparative diagnoses of the two Recent 

 subfamilies follows: 



Hollardiinae. The dorsal surface of the supraoccipital 

 entirely domelike, without a broad flat expanse, the pos- 

 terior surface of the dome convex; epiotics not meeting 

 medially on the dorsal surface of the skull, separated 

 there by the supraoccipital and meeting medially only on 

 the posterior surface of the skull, and articulating 

 anteriorly with the frontals; pelvis a sturdy shaft more or 

 less triangular or broadly heart-shaped in cross section; 

 first anal fin basal pterygiophore tending to be -t- -shaped 

 in cross section, with an anteromedial process; teeth con- 

 ical. Four western Atlantic species and one from Hawaii, 

 in two genera (Hollardia and Parahollardia) . 



Comparative diagnoses of subfamilies (Spinacan- 

 thinae, Eoplectinae, Hollardiinae, Triacanthodinae). 



—As discussed in greater detail by Tyler (1968, 1973b), 

 there are four subfamilies of triacanthodids, two fossil, 

 and two Recent, whose most pertinent diagnostic 

 features are summarized below. See Sorbini (1968) and 

 Blot (1969) for the upper portion of the lower Eocene 

 age of the Monte Bolca, Italy, fish beds. 



The Eocene Spinacanthinae differ from both the 

 Eocene Eoplectinae and the Recent species (Hollardiinae 

 and Triacanthodinae) in having: enormously elongate 

 dorsal fin spines (50 to 90% SL) in an exceptionally long- 

 based fin (slightly over 50% SL), with the soft dorsal and 

 anal fins exceptionally short-based (about 11 to 12% SL); 

 the spiny dorsal fin origin over the level of the middle or 

 front of the eye; the eye small (5 to 7% SL) and placed 

 high in the head; a probably only poorly developed 



Triacanthodinae. The dorsal surface of the supraoc- 

 cipital with a broad flat expanse, anteromedially on 

 which is an upraised area varying in shape from a small 

 dome to a laterally compressed thin crest; epiotics 

 meeting medially on the dorsal surface of the skull as 

 well as on the posterior surface, and separated anteriorly 

 from the frontals by the sphenotics; pelvis a flat basin 

 with upturned edges; first anal fin basal pterygiophore 

 T-shaped in cross section, without an anteromedial 

 process; teeth conical or wider than thick and more or 

 less truncate distally. Of the 14 species in 9 genera, 13 

 species belong to 8 genera (Triacanthodes, Mephisto, 

 Paratriacanthodes, Atrophacanthus, Bathyphylax, 

 Tydemania, Macrorhamphosodes, Halimochirurgus) in 

 the Indo-western Pacific, and 1 species belongs to a 

 monotypic genus (Johnsonina) in the western Atlantic. 



Anatomical diversity. — The anatomical diversity of 

 the two Recent subfamilies has been treated in detail by 



