pterygiophore + -shaped in cross section; well developed 

 lateral flanges for muscle attachment present along most 

 of the length of most of the basal pterygiophores of the 

 soft dorsal and anal fins; a sturdy lateral flange present 

 horizontally along the middle of the posterior half of the 

 last centrum and the anterior region of the hypural 

 plate; soft dorsal fin basal pterygiophores 20-26, anal fin 

 basal pterygiophores 14-19, most of these pterygiophores 

 sutured to one another distally; distal pterygiophores of 

 soft dorsal and anal fins often unossified, the ossifica- 

 tion, when present, always as a single piece and not as a 

 pair of elements to either side of the midline; sixth dor- 

 sal spine nearly always present as a rudiment, in all but 

 very young specimens usually as a splint of bone buried 

 beneath the skin, but sometimes protruding to the sur- 

 face even in adults; the fifth spine usually very short, but 

 nearly always protruding at least a short distance 

 through the skin; the first four spines always visible ex- 

 ternally, but the fifth and sixth spines sometimes absent 

 in one Recent species and perhaps in several fossil forms; 

 dorsal fin rays 19-26; anal fin rays 13-22; pelvic fin with a 

 large spine followed in some species by a single ray which 

 becomes a buried rudiment in adults; adults never with a 

 protruding pelvic ray; dorsal and pelvic spines with 

 numerous shallow lengthwise grooves (except in the 

 Miocene Marosichthys, in which the grooves seem to be 

 deep), mostly obscured by the overlying scale plates ex- 

 cept at the naked distal end (one-tenth or less of the 

 length); uppermost pectoral fin ray nubbinlike, the two 

 halves of the ray about equally short or the lateral half 

 shorter, the basal region of the medial half always im- 

 mensely larger than that of the lateral half; the slightly 

 overlapping basal plates of the scales of the body bearing 

 either an emarginate cruciform ridge or an anterior to 

 posterior series of vertical emarginate ridges (except in 

 the Eocene Protacanthodes, with numerous upright 

 spinules, and in the Oligocene Cryptobalistes, without 

 elaborate ornamentation); peritoneum pale, often with 

 silvery overtones; coloration basically silvery-gray, with 

 yellowish or greenish overtones; lateral line relatively 

 conspicuous (least so in Trixiphichthys weberi); scaly 

 skin forming a definite low sheath along the bases of the 

 soft dorsal and anal fins; olfactory lamellae 23-54, 

 relatively thin; anterior nostril with an upraised rim pos- 

 teriorly, essentially flush with the surface anteriorly, the 

 rim not tubelike; posterior nostril with an upraised rim 

 anteriorly; gill rakers laterally on first arch relatively 

 short, shorter than the width of the fleshy arch; usually 

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

 the first arch above the angle; caudal peduncle relatively 

 long, 16 to 31% SL, distinctly tapering to a narrow trans- 

 versely indented region above and below just in front of 

 the caudal fin base (except in the Eocene 

 Protacanthodes, which has a relatively deep and only 

 slightly tapered peduncle); least depth of the caudal 

 peduncle, between the precaudal grooves, 2 to 5% SL (ex- 

 cept in the Eocene Protacanthodes, the depth 15% SL, 

 and in the Oligocene Acanthopleurus collettei, the depth 

 5 to 8% SL, versus 4 to 5% SL in the Oligocene A. ser- 

 ratus and 2 to 4% SL in Recent species); the caudal 



peduncle wider than deep at this point (except in A. col- 

 lettei, the width probably about equal to the depth, and 

 in the Eocene Protacanthodes, the width unknown but 

 obviously less than the depth); caudal fin deeply forked 

 (except in the fossil genera Protacanthodes, with a 

 rounded caudal, and Cryptobalistes, with an almost 

 truncate caudal). 



Figure 32.~Pseudotriacanthus strigilifer: 



showing the course of the lateral line; lower 



left, scales from upper middle region of 



body, including two lateral line canal 



bearing scales: lower right, nasal 



region as seen externally (above) and 



the olfactory lamellae as seen with the top 



of the nasal sac removed. 



Detailed description o{ Pseudotriacanthus atrigilifer. 



Material examined. — Five cleared and stained speci- 

 mens, 79.0-145 mm. 



Occipital Region. 



Basioccipital. — A short column, dorsolateral^ 

 expanded; cartilage filled along its anterior and antero- 

 dorsal edges; articulates by extensive interdigitation 

 posterolaterally with the exoccipitals, anterolaterally 

 with the prootics and anteroventrally with the overlying 

 posterior end of the parasphenoid. The rim of the round 

 concave posterior end of the basioccipital articulates by 

 fibrous tissue with the rim of the concave anterior face of 

 the centrum of the first vertebra. A deeply concave 

 medial channel is present on the anterior three-fourths of 

 the ventral surface of the basioccipital. The anterior end 

 of this channel is mostly hidden from view by the overly- 

 ing parasphenoid. Posteriorly this channel is open to the 



