caudal vertebrae. The pterygial elements are cartilage 

 filled at their dorsal and ventral ends. 



Anal Fin. 



Fin rays and pterygiophores. — Usually 15 or 16 fin 

 rays are present; the first ray and sometimes the second 

 ray unbranched, the others branched in single to double 

 dichotomies. No ossified distal pterygiophores are pres- 

 ent between the bifurcate bases of the rays. Basally the 

 fin rays are supported by a number of basal pterygio- 

 phores equal to or sometimes one less than the number of 

 rays. The pterygiophores articulate to one another by ex- 

 tensive interdigitation in a manner similar to that 

 described for the basal pterygiophores of the soft dorsal 

 fin and possess holes distally between the apposed 

 anterior and posterior edges of the pterygiophores, at 

 least anteriorly in the series. Well-developed lateral 

 flanges with hooklike processes are present just as with 

 the basal pterygiophores of the soft dorsal fin. The first 

 basal pterygiophore of the anal fin is by far the largest of 

 the series, the others decreasing in length posteriorly in 

 the series. There is a prominent crest anterodistally on 

 the first basal pterygiophore of the anal fin in addition to 

 the lateral flange similar to that which is present on the 

 other basal pterygiophores. The first basal pterygio- 

 phore is held immovably by fibrous tissue against the 

 posterior edge of the haemal spine of the ninth vertebra, 

 making the latter by definition the first caudal 

 vertebra. The last several basal pterygiophores of the 

 anal fin articulate by fibrous tissue between the neural 

 spines of the fifth and sixth caudal vertebrae, just as the 

 last few basal pterygiophores of the soft dorsal fin are 

 held between the neural spines of the same two 

 vertebrae. 



Comparative diagnoses of subfamilies (Protacan- 

 thodinae, Cryptobalistinae, Triacanthinae). — There 

 are three subfamilies of triacanthids: two exclusively 

 fossil (one from the Eocene and one from the Oligocene) 

 and one with both fossil (Oligocene and Miocene) and 

 Recent species. These three subfamilies are compara- 

 tively diagnosed as follows, modified and expanded 

 from Tyler (1968), especially on the basis of the reexami- 

 nation of the holotype of the Eocene Protacanthodes. 



The Eocene Protacanthodinae have: the pelvis 

 shaftlike posterior to the region of the pelvic spines and 

 probably not bifurcate anterior to the spines and of un- 

 known cross-sectional shape; the spiny dorsal fin base 

 slightly longer than the soft dorsal fin base; six ab- 

 dominal vertebrae anterior to the first basal pterygio- 

 phore of the soft dorsal fin; second to fourth basal 

 pterygiophores of the spiny dorsal fin with well- 

 developed ventral shafts oriented more or less vertically 

 in relation to the vertebral axis and with their proximal 

 ends in contact with the distal ends of the neural spines 

 of the second to fourth abdominal vertebrae; ventrally 

 directed portion of the first basal pterygiophore of the 

 spiny dorsal fin long and well developed, articulated 



with the middle to basal region of the posterior surface of 

 the skull; most neural spines relatively oblique; skeletal 

 appearance similar to that of the Recent triacanthids 

 and not to that of balistids; caudal peduncle only slightly 

 tapering toward the tail, deeper than wide at the place of 

 least depth; caudal fin extremely long (53% SL) and 

 rounded; scales with numerous upright spinules. A single 

 species, Protacanthodes ombonii (Zigno 1887a). 



The Oligocene Cryptobalistinae have: the pelvis 

 basinlike from the region of the pelvic spines posteriorly, 

 but bifurcate anterior to the spines; pelvis in cross section 

 behind the pelvic spines flat, with upturned edges form- 

 ing a concave dorsal surface, wider than deep; spiny dor- 

 sal fin base much shorter than the soft dorsal fin base; 

 probably six abdominal vertebrae anterior to the first 

 basal pterygiophore of the soft dorsal fin; second to third 

 (fourth, if present, unknown) basal pterygiophores of the 

 spiny dorsal fin essentially without ventral shafts, these 

 pterygiophores far removed from the distal ends of the 

 neural spines of the abdominal vertebrae; ventrally 

 directed portion of the first basal pterygiophore of the 

 spiny dorsal fin very short, articulated with the upper 

 region of the posterior surface of the skull; most neural 

 spines relatively vertical; skeletal appearance generally 

 similar to that of the balistids rather than to that of Re- 

 cent triacanthids; caudal peduncle probably tapered to a 

 constricted region in front of the caudal fin, and probably 

 about as wide as deep; caudal fin of moderate length 

 (31% SL), basically truncate, with a slight medial con- 

 cavity; scales apparently without elaborate ornamenta- 

 tion. A single species, Cryptobalistes brevis (Rath 1859). 



The Oligocene to Recent Triacanthinae have: the 

 pelvis shaftlike from the region of the pelvic spines pos- 

 teriorly and not bifurcate anterior to the spines; pelvis in 

 cross section behind the pelvic spines like a railroad rail, 

 deeper than wide or at least about as deep as wide, the 

 lateral edges not upturned; spiny dorsal fin base much 

 shorter than the soft dorsal fin base; four or five ab- 

 dominal vertebrae anterior to the first basal pterygio- 

 phore of the soft dorsal fin; second to fifth basal pterygio- 

 phores of the spiny dorsal fin with moderately developed 

 ventral shafts, usually directed anteroventrally toward 

 the region between the neural spines of the first to third 

 abdominal vertebrae but not in direct contact with them, 

 usually well separated from them; ventrally directed 

 shaft of the first basal pterygiophore of the spiny dorsal 

 fin long and well developed, articulated with the middle 

 to basal region of the posterior surface of the skull; most 

 neural spines relatively oblique; skeletal appearance 

 similar to that of the Recent triacanthids and not to that 

 of balistids; caudal peduncle tapered to a narrow trans- 

 versely indented region above and below in front of the 

 caudal fin, wider than deep at this point; caudal fin of 

 short to moderate length (15 to 30% SL), deeply forked; 

 scales with low emarginate ridges. Seven Recent species 

 in four genera (Triacanthus, Trixiphichthys, Pseudotria- 

 canthus, Tripodichthys) in the Indo-western Pacific, two 

 fossil species in a single Oligocene genus (Acantho- 

 pleurus), and one species from the Miocene (Maro- 

 sichthys). 



