placed anterior to first basal pterygiophore of soft dorsal 

 fin (the Eocene Eoplectus with nine abdominal verte- 

 brae, all but the last with their neural spines anterior to 

 the first soft dorsal fin basal pterygiophore); first anal fin 

 basal pterygiophore either with or without a medial 

 flange anterior to its lateral flanges, the pterygiophore 

 either T- or + -shaped in cross section; well-developed 

 lateral flanges for muscle attachment present only on the 

 first anal fin basal pterygiophore, those present, if any, 

 on the other pterygiophores very poorly developed; no 

 lateral flange present horizontally along the last cen- 

 trum or on the hypurals; soft dorsal fin basal pterygio- 

 phores 11 to 16, anal fin basal pterygiophores 11 to 13, 

 these pterygiophores not sutured to one another distally 

 (probably fewer basal pterygiophores in both fins in the 

 Eocene Spinacanthus); distal pterygiophores of soft dor- 

 sal and anal fins always ossified in adults, usually as two 

 separate halves; sixth dorsal spine either a short 

 (probably longer in the Eocene Spinacanthus) 

 protruding element or a rudiment buried beneath the 

 skin or barely protruding to the surface; third to fifth 

 spines either normally developed or rudiments buried 

 beneath the skin or barely protruding to the surface; first 

 and second spines always prominent and visible exter- 

 nally; dorsal fin rays 12 to 18; anal fin rays 11 to 16 (fewer 

 rays in both fins in the Eocene Spinacanthus); pelvic fin 

 with a large (smaller in the Eocene Protobalistum and 

 Spinacanthus) spine followed in the Eocene Eoplectus by 

 four well-developed branched rays but in all Recent 

 species by no more than one or two small unbranched 

 rays, both of which, but especially the second, become in 

 some species buried rudiments in adults; adults of some 

 species with one or two protruding pelvic rays; dorsal and 

 pelvic spines with deep lengthwise grooves, obscured by 

 the overlying scale plates except at the naked distal end 

 (one-half to one-tenth or less of the length); uppermost 

 pectoral fin ray short but not reduced to a nubbin, the 

 two halves of the ray of about equal length and the basal 

 region of the medial half not immensely larger than that 

 of the lateral half; the slightly overlapping basal plates of 

 the scales of the body bearing a vertical row of upright 

 spinules arising from individual bases, large specimens of 

 some species acquiring supplemental spinules in front of 

 and behind the principal row (the Eocene Eoplectus with 

 a single upright spinule per scale plate and the body not 

 completely covered with scales, some of the plates being 

 isolated and nonoverlapping, and the Eocene Protobalis- 



Figure 4.— Range of diversity in body form in the 



Recent Triacanthodidae: Parahollardia Uneata (left) 



and Halimochirurgus alcocki (right). 



turn with huge more or less hexagonal plates bearing 

 numerous rounded tubercules, as in ostracioids); 

 peritoneum light tan to jet black, except in Hollardia 

 meadi in which it is pale or silvery; coloration basically 

 reddish, often with darker red, blue, yellow, or green 

 markings; lateral line inconspicuous; scaly skin not form- 

 ing a definite low sheath along the bases of the soft dor- 

 sal and anal fins; olfactory lamellae 9 to 20, relatively 

 plump; anterior nostril with a tube, lowest in front, 

 highest in back; posterior nostril more or less flush with 

 the surface, or with a slightly upraised rim anteriorly; gill 

 rakers laterally on first arch relatively long, as long as or 

 longer than the width of the fleshy arch; two to seven, 

 rarely only one, rakers laterally on the upper limb of the 

 first arch above the angle; caudal peduncle relatively 

 short, 10 to 19'^c SL (24'~c SL in the Eocene Eoplectus), 

 not distinctly tapered and without a narrow transversely 

 indented region above and below just in front of the 

 caudal fin base; least depth of the caudal peduncle 5 to 

 12'^c SL (21% SL in the Eocene Eoplectus); caudal 

 peduncle deeper than wide; caudal fin rounded to al- 

 most truncate. 



Detailed description of Parahollardia Uneata. 



Material examined. — Seven cleared and stained 

 specimens, 4.5.7-86.1 mm. The large amounts of cartilage 

 visible on the surface of the skull, particularly in the otic 

 and occipital regions, is the norm for the family, in con- 

 trast to the closely related and derivative Triacanthidae. 

 Even as large specimens, all species of Triacanthodidae 

 retain cartilaginous regions between some of the cranial 

 bones, although the amount slightly decreases with in- 

 creasing specimen size. The largest specimen of a Recent 

 triacanthodid presently recorded (Tyler 1968:64) is a 174 

 mm female Hollardia hollardi (ANSP 97654) which has 

 subsequently been cleared and stained. As can be seen in 

 Figure 22, areas of cartilage are still present on the sur- 

 face of the skull in the occipital and otic regions, al- 

 though the various bones are more extensively inter- 

 digitated to one another than in the 62.7 mm specimen 

 illustrated by Tyler (1968:fig. 198) and relatively less car- 

 tilage is present. 



SKULL. 



Occipital Region. 



Basioccipital. — A short column, dorsolateral^ ex- 

 panded; cartilage filled along its anterior and anterodor- 

 sal edges; articulates through cartilage posterolaterally 



