more regular interlocking emarginations; sphenotic rela- 

 tively small and confined to the posterior wall of the or- 

 bit, not reaching the lateral or dorsal surface of the skull; 

 first branchiostegal ray with its dorsal edge slightly in- 

 tumed, articulated with the ventrolateral surface of the 

 ceratohyal; interoperculum with a ventral flange and a 

 short posterior shaft extending only slightly behind the 

 ventral flange and level of the epihyal; pterotic prolonged 

 posteroventrally as a stout laterally compressed shaft 

 broadly articulating with the hyomandibular and supra- 

 cleithrum; epiotic confined to the lateral region of the top 

 of the skull, separated from the supraoccipital by the 

 exoccipital; exoccipital in contact with the frontal; fron- 

 tal in contact posteriorly with the pterotic in the rear of 

 the orbit; olfactory epithelium in the form of a rosette, 

 the lamellae radiating out from a horseshoe-shaped base, 

 the olfactory sac below the surface of the body and the 

 two nostrils more or less flush with the surface, the 

 anterior nostril with an upraised flap posteriorly and the 

 posterior nostril with an upraised flap anteriorly. 



Detailed description of Triodon macropterus. 



Material examined. — Two cleared and stained 

 specimens, 391-463 mm. It will be advantageous in the 

 future to compare the amount of interdigitation in the 

 skull structure of these two large adult specimens with 

 that in a young specimen, but the species as yet is known 

 only from several dozen relatively large (about 285-480 

 mm, see Tyler 1967:90) adults. This species has often 

 been called T. bursarius, but Boeseman (1962) has thor- 

 oughly reviewed the literature £md shown T. macropterus 

 to have priority. 



SKULL. 



Occipital Region. 



Basioccipital. — A very short column, slightly 

 expanded anterodorsally; cartilage filled at its anterior 

 ledge; articulates by extensive interdigitation anteriorly 

 with the overlying parasphenoid, anterolaterally with the 

 prootics, and posterolaterally with the exoccipitals. A 

 slight depression is present medially on the ventral sur- 

 face of the anterior end of the basioccipital just behind 

 the region where it is overlain by the parasphenoid. This 

 depression continues anteriorly as a narrow canal 

 between the otherwise interdigitated surfaces of the 

 basioccipital and parasphenoid, and opens into the ex- 

 treme posterior end of the myodome. The extreme pos- 

 teroventral portion of the wall of the myodome is formed 

 by the anterodorsal end of the basioccipital. The rim of 

 the round concave posterior end of the basioccipital ar- 

 ticulates by fibrous tissue with the rim of the concave 

 anterior face of the centrum of the first vertebra. 



Exoccipital. —Extremely large; cartilage filled 

 along its dorsal and dorsolateral edges; articulates by ex- 

 tensive interdigitation dorsomedially with the supra- 

 occipital, anterodorsally with the frontal, dorsolaterally 



Figure 181. — Triodon macropterus: showing the course 



of the lateral line; lower left, the nasal region as 



seen externally (above) and the olfactory lamellae 



as seen with the top of the nasal sac removed; lower 



right, scales from upper middle region of body, 



including three lateral line canal bearing scales. 



with the epiotic and pterotic, ventrolaterally with the 

 prootic, and ventromedially with the basioccipital. The 

 posteromedial edges of the two exoccipitals form the ven- 

 tral and lateral walls of the foramen magnum, while dor- 

 sally the wall of the foramen is formed mostly by the 

 exoccipitals, but also for a short distance medially by the 

 ventral edge of the supraoccipital. Strong condyles pro- 

 ject from the posteromedial portions of the exoccipitals 

 and make fibrous tissue contact over the anterior half of 

 the lateral surfaces of the centrum of the first vertebra. 



Supraoccipital. —Somewhat expanded anteriorly, 

 but drawn out into a short, stout, laterally compressed 

 spine posteriorly; cartilage filled along all of its edges of 

 articulation with the other cranial bones, except pos- 

 teroventrally; articulates by interdigitation anteriorly 

 and anterolaterally with the frontals and postero- 

 laterally with the exoccipitals. 



Otic Region. 



Pterotic. — Very large; cartilage filled along its 

 medial edge; articulates by interdigitation anterodor- 

 sally with the epiotic, anteroventrally with the 

 sphenotic, ventromedially with the prootic, and postero- 

 medially with the exoccipital. Posteroventrally the 

 pterotic is prolonged into a stout, laterally compressed 

 shaft which articulates by fibrous tissue along its ante- 

 rior edge with the hyomandibular and along its posterior 

 edge with the supracleithrum. The articulation with the 

 supracleithrum appears to also involve some interdigi- 

 tation in the smaller specimen, but not in the larger; in 

 neither case is the articulation very flexible. The more 

 normal articulation of the pterotic with the supracleith- 

 rum is through fibrous tissue along the slightly concave 

 ventral surface of the extreme posterodorsal region of the 

 pterotic. Just anterior to the base of its stout shaft the 

 pterotic is deeply concave to receive and articulate by fi- 

 brous tissue with most of the length of the dorsal end of 

 the hyomandibular. 



