FISHERY BULLETIN: VOL. 79, NO. 3 



Vertebrae and caudal skeleton (Figure 12). — In 

 the two cleared and stained specimens of T. 

 ocellatum examined, there are 22 vertebrae (in- 

 cluding the last centrum to which is fused the 

 hypural plate; Pietsch 1972:38). Preural centra 2 

 through 18 bear complete haemal arches and are 

 considered caudal vertebrae. The neural spines of 

 preural centra 14 through 22 are considerably 

 shorter than those of the more posterior centra; 

 correspondingly, the seven anteriormost proximal 

 radials of the soft dorsal fin are also short so that 

 they do not interdigitate with the respective 

 neural spines. Further, there appears to be little if 

 any connective tissue between the elements of the 

 soft dorsal fin and the vertebral column in this 

 region allowing for independent movement of the 

 anterior portion of the fin relative to the axial 

 skeleton. The haemal spines of preural centra 14 

 through 17 are unusually broad and laterally 

 compressed. 



The hypural plate, slightly notched posteriorly, 

 bears the overlapping bases of nine principle 

 caudal rays. The central seven caudal rays are 

 bifurcated distally. There are no epurals. 



Median fins and illicial apparatus (Figures 12, 

 13). — The spinous dorsal fin consists of three 

 spines. The anteriormost two are supported by a 

 single, elongate, horizontally situated pterygio- 

 phore (Figure 13) that is loosely attached to the 

 dorsal surface of the cranium between the anterior 

 halves of the frontal bones by three pairs of 

 extrinsic illicial muscles (Bertelsen 1951:18, fig. 4; 



Illicial 



Spine II 



Pterygiophore 

 of illicium 



Figure l.'^ — Spinous dorsal fin of Tetrahrachiiim ocellatum. 

 AMS IB.7178, 61 mm SL: A. Illicial apparatus, second dorsal 

 spine, and common pterygiophore; B. Third dorsal spine and 

 pterygiophore. 



Bradbury 1967, fig. 2; Winterbottom 1974:284, fig. 

 44). The illicial bone (Bradbury 1967:401) is con- 

 siderably reduced in size relative to other lophi- 

 iforms (Gregory 1933, fig. 265, 266, 267; Pietsch 

 1972, 1974, 1979). The second spine is considerably 

 thicker and approximately three times longer 

 than the first. The third spine, slightly longer 

 and thicker than the second, is supported by a 

 second, elongate, and horizontally placed, cephalic 

 pterygiophore that is tightly connected to the 

 posterior, dorsomedial surface of the supraoccip- 

 ital and anterior, dorsomedial margins of the 

 epiotics. The proximal end of each spine is bifur- 

 cated, each fork bearing a small, medially directed 

 prong; the prongs of each spine fit within a large, 

 rounded foramen located on a highly compressed, 

 bladelike dorsal expansion of the respective 

 pterygiophore. 



The soft dorsal fi.n consists of 16 biserial, seg- 

 mented, and unbranched rays, each supported by 

 a cartilaginous distal radial and an ossified prox- 

 imal radial. The proximal end of the anteriormost 

 proximal radial lies above the neural spine of the 

 19th preural centrum, while the proximal end of 

 the last proximal radial lies between the neural 

 spines of the fourth and fifth preural centra. 



The anal fin consists of 11 biserial, segmented, 

 and unbranched rays. The first two rays share a 

 single supporting radial. The remaining rays are 

 each supported by a small, cartilaginous distal 

 radial and an elongate, ossified proximal radial. 

 The proximal ends of the two anteriormost prox- 

 imal radials lie between the haemal spines of the 

 12th and 13th preural centra. The proximal radials 

 of the nine remaining anal fin rays have a one-to- 

 one correspondence with the haemal spines, so 

 that the radial of the last anal ray lies between the 

 haemal spines of the fourth and fifth preural 

 centra. The posteriormost rays of the dorsal and 

 anal fins are broadly connected by a membrane to 

 the dorsal and ventral margins of the caudal fin 

 so that a caudal peduncle is absent. 



Pectoral and pelvic girdles and fins (Figure 14). — 

 The posttemporal is unusually large and con- 

 nected to the posterolateral corner of the cranium 

 in such a way as to allow for considerable move- 

 ment (relative to the cranium) in an anterodorsal- 

 posteroventral plane. The bone consists of a broad, 

 dorsal flange that overlaps the dorsolateral sur- 

 face of the epiotic, pterotic, and exoccipital. A 

 large ligament originates on the posterodorsal 

 margin of the prootic and inserts on the tip of 



396 



