dorsal fin muscle mass. There are 18 dorsal fin rays pres- 

 ent anterior to the first dorsal fin ray supported by a 

 modified dorsal fin basal pterygiophore posterior to the 

 neural spine of the seventh caudal vertebra. The first five 

 dorsal fin rays are unbranched, and the sixth ray is only 

 slightly branched at its extreme distal end. The 7th to 

 16th fin rays are extensively branched distally, so much 

 so that some of the rays have over 50 terminal segments 

 (incomplete sextuple dichotomies). The right and left 

 halves of each of the rays are well-separated by fibrous 

 tissue from one another medially throughout their 

 lengths, except distally where they begin to branch. As 

 with the pectoral fin rays, cross-striations are only pres- 

 ent extremely distally on some of the branches as poorly 

 defined articulations. The bifurcate bases of the dorsal 

 fin rays enclose plugs of calcified cartilage which articu- 

 late by fibrous tissue with the cartilaginous plate below 

 them. There are thus three series of pterygial elements 

 supptorting the dorsal fin rays: 1) the ossified basal 

 pterygiophores; 2) the partially calcified cartilaginous 

 plate representing the closely apposed or confluent 

 medial pterygiophores; and 3) the calcified cartilagi- 

 nous plugs or distal pterygiophores at the bifurcate bases 

 of the fin rays. 



Except for the anteriormost pterygiophore, the nine 

 anal fin basal pterygiophores are like those of the dorsal 

 fin, except longer. They have concave proximal ends 

 which are cartilage filled and they articulate by fibrous 

 tissue with the haemal spines of the caudal vertebrae and 

 with one another. Their distal ends are irregularly carti- 

 lage filled and closely apposed or continuous with the 

 partially calcified cartilaginous plate that intervenes 

 between them and the anal fin rays. The first anal fin 

 basal pterygiophore is deeply concave along the poste- 

 rior surface of the upper two-thirds of its length where it 

 overlies and articulates by fibrous tissue with the hae- 

 mal spines of the first two caudal vertebrae. Distally the 

 first basal pterygiophore is bifurcate into two parts which 

 fit against the medial pterygial plate. The medial ptery- 

 gial plate is, like the dorsal fin medial pterygial plate, 

 irregularly calcified. Sixteen anal fin rays are present 

 anterior to the first anal fin ray supported by a modified 

 basal pterygiophore posterior to the haemal spine of the 

 seventh caudal vertebra. The first five anal fin rays are 

 unbranched, and the sixth is only slightly branched dis- 

 tally. The 7th to 15th anal fin rays are branched in the 

 same extensive manner as the corresponding rays of the 

 dorsal fin. The 16th anal fin ray is much less branched 

 than those anterior to it. The anal fin rays have the same 

 structure as those of the dorsal fin and likewise have 

 plugs of calcified cartilage, or distal pterygiophores, 

 embedded between their bifurcate bases. 



Posterior to the neural spine of the seventh caudal ver- 

 tebra there are seven modified dorsal fin basal pterygio- 

 phores which distally support the seven dorsal fin rays of 

 the upper half of the pseudocaudal fin. The uppermost, ' 

 or first, modified basal pterygiophore is placed at about a 

 right angle to the vertebral column, but the second to 

 seventh modified basal pterygiophores are progressively 

 more obliquely placed, until the seventh is almost 



parallel to the vertebral column. Except for the first, 

 these modified basal pterygiophores are cartilage filled at 

 both ends and articulate by fibrous tissue proximally 

 with the neural spines of the seventh or eighth caudal 

 vertebrae and distally with the blocks of calcified carti- 

 lage that form the medial pterygiophores of the pseudo- 

 caudal fin. The proximal ends of the second to fifth mod- 

 ified basal pterygiophores articulate with the posterior 

 edge of the neural spine of the seventh caudal vertebra, 

 while the proximal ends of the sixth and seventh modi- 

 fied basal pterygiophores articulate with the posterior 

 edge of the neural spine of the eighth caudal vertebra. 

 The proximal end of the first modified basal pterygio- 

 phore tapers to a narrow shaft articulated by fibrous tis- 

 sue with the posterior edge of the last unmodified dorsal 

 fin basal pterygiophore. The distal end of the first modi- 

 fied basal pterygiophore articulates with the postero- 

 ventral edge of the large, partially calcified, cartilagi- 

 nous mass that makes up the medial pterygiophore of the 

 dorsal fin. The medial pterygiophore above the second 

 modified basal pterygiophore is also continuous with the 

 medial pterygiophore of the dorsal fin, being delimited 

 from it only by a constricted region of cartilage. The cal- 

 cified cartilages of the medial pterygiophores at the dis- 

 tal ends of the third to sixth modified basal pterygio- 

 phores remain separate from one another in the two 

 cleared and stained specimens. The medial pterygio- 

 phore of the modified seventh basal pterygiophore is con- 

 nected with the cartilage at the end of the ninth caudal 

 vertebra and with the medial pterygiophore of the eighth 

 modified anal fin basal pterygiophore. It is to be expect- 

 ed that in larger specimens more of the medial pterygio- 

 phores of the pseudocaudal fin become continuous with 

 one another, because even in the two relatively small 

 study specimens, the short, thin processes of the fifth 

 and sixth medial pterygiophores almost make contact 

 with the medial pterygiophores below them. The distal 

 pterygiophores of the pseudocaudal fin, whose postero- 

 lateral surfaces are overlain by the bifurcate bases of the 

 fin rays, are blocks of calcified cartilage which increase in 

 size in the series from that distal to the first to that dis- 

 tal to the seventh modified basal pterygiophore. The dis- 

 tal pterygiophores are thickest at their ends which artic- 

 ulate by fibrous tissue with the medial pterygiophores. 

 The seven fin rays supported by the distal pterygio- 

 phores increase slightly in length in the series from that 

 attached to the first to that attached to the seventh 

 pterygiophore. The fin ray above the first modified basal 

 pterygiophore is branched in a double dichotomy, but 

 the other rays of the pseudocaudal fin are simply divided 

 into two terminal segments. None of the fin rays are 

 cross-striated. In the two study specimens, bony ossicles 

 are just beginning to be evident around the bifurcate dis- 

 tal ends of a few of the more medial rays of the pseudo- 

 caudal fin, these ossicles being well developed in adults. 

 The anal fin portion of the pseudocaudal fin has basi- 

 cally the same structure as the dorsal fin portion. How- 

 ever, since eight modified anal fin basal pterygiophores 

 are present, rather than seven modified basal pterygio- 

 phores as in the dorsal portion, there are eight anal fin 



