Figure i\ .—Trixiphichthya weberi: latei 

 head, 101 mm SL. Bay of Bengal 



spicuous in Trixiphichthys than in the other three 

 genera. The second dorsal fin spine is best developed in 

 Pseudotriacanthus (greater than half the length of the 

 first spine), next best developed in Trixiphichthys 

 (about half the length of the first spine) and relatively 

 short in the other two genera (about one-third or less the 

 length of the first spine). The scales in Pseudotria- 

 canthus have an anterior to posterior series of high thin 

 distally emarginate vertical ridges, while in the other 

 three genera the scales have a low, distally emarginate 

 cruciform ridge. The shaft of the pelvis posterior to the 

 pelvic spines tapers to a sharp point posteriorly in 

 Pseudotriacanthus and Tripodichthys, but does not 

 taper to a sharp point in Triacanthus and Trixi- 

 phichthys. The length of the anal fin base is shorter 

 (usually about 2 times in the soft dorsal fin base) in 

 Pseudotriacanthus than in the other three genera (usual- 

 ly about 1.4 to 1.7 times in the soft dorsal fin base). The 

 lateral edge of the sagitta is relatively straight or 

 somewhat convex in Triacanthus, but has a distinct in- 

 dentation or cavity in the other three genera. The base of 

 the pseudobranch has a forward pointed apex about one- 

 third down its length in Trixiphichthys but is an even 

 curve without an apex in the other three genera, which 

 usually have a shorter base to the pseudobranch and 

 fewer lamellae. There are fewer dorsal, anal, and pectoral 

 fin rays in Pseudotriacanthus than in the other three 

 genera. The sixth, and last, dorsal fin spine is more often 

 completely lost in Triacanthus biaculeatus than in the 

 other six species. Externally visible rudiments of the 

 pelvic fin ray buried in the skin are retained longer in 

 Tripodichthys oxycephalus than in the other six species. 

 The fossil triacanthids include at least one genus 

 highly similar to the Recent species, another genus 



highly dissimilar to the Recent species, and one genus 

 obviously intermediate in many respects between the 

 triacanthodids and triacanthids. These were treated by 

 Tyler ( 1968) mainly on the basis of the literature, but 

 some of the specimens have subsequently been re- 

 examined, and notes are given here on their anatomy. 



The Eocene Protacanthodes ombonii, the only repre- 

 sentative of the Protacanthodinae, is known from a single 

 specimen which has recently been reexamined. The 

 holotypic specimen, in counterpart, IGUP 10.901 (head 

 to left) - 902, from the upper portion of the lower Eocene 

 of Monte Bolca, Italy, is 112 mm SL, an excellent im- 

 pression with well-preserved scales that obscure many 

 osteological features. 



Proportional measurements (percent of standard 

 length in parentheses) for P. ombonii are: greatest 

 depth 45.7 mm (40.7% SL); snout to base of first dorsal 

 spine 44.2 mm (39.3% SL); eye 11.4 mm (10.1% SL); 

 spiny dorsal fin base 25.8 mm (23.0% SL); soft dorsal fin 

 base 23.5 mm (20.9% SL); anal fin base 12.4 mm (11.0% 

 SL); daudal peduncle length 26.2 mm (23.3% SL); least 

 caudal peduncle depth 16.4 mm (14.6% SL); caudal fin 

 length 50.6 mm (45.0% SL); length of pelvis posterior to 

 the base of the pelvic spine 17.9 mm (15.9% SL); length 

 of pelvic spine 27.9 mm (24.8% SL); soft dorsal fin height 

 10.5 mm (9.3% SL); anal fin height 10.0 mm (8.9% SL); 

 and the approximate lengths of the dorsal fin spines are 

 as follows: first 36.5 mm (2.5% SL), second 10.5 mm 

 (9.3% SL), third 6.0 mm (5.3% SL), fourth 5.0 mm (4.4% 

 SL), fifth 1.9 mm (1.7% SL), sixth 1.4 mm (1.2% SL). 



The six dorsal spines, which decrease greatly in length 

 posteriorly in the series, are followed by 19 fin rays, the 

 distal ends of those that show being branched. The dis- 

 tance between the last spine and the first ray (5.1 mm, 



