pair of pieces and another has three small pieces, as dis- 

 cussed by Tyler (1970b:5). The second pair of uroneurals 

 is represented by two long separate pieces in three of the 

 specimens, while in the other three specimens the two 

 halves are fully fused anteriorly. 



The hypurals decrease in length from the first (lower- 

 most) to the fifth. Fifth hypural directed posterodorsally 

 from just behind and slightly below the uppermost point 

 of the urostyle; more or less rod-shaped; supports, along 

 with the uppermost edge of the fourth hypural, the up- 

 permost caudal fin ray. Fourth hypural the deepest of the 

 hypural elements; articulates anteriorly with the pos- 

 terior edge of the urostyle and posteriorly supports the 

 uppermost five caudal fin rays, although it shares the 

 support of the uppermost and lowermost of these five 

 rays with, respectively, the fifth hypural and third 

 hypural. Third hypural broad posteriorly but becoming 

 narrow anteriorly where it articulates with the posterior 

 edge of the urostyle; posteriorly it supports the upper of 

 the middle two caudal fin rays and partially supports the 

 lowermost of the upper five caudal fin rays. Second 

 hypural similar to third hypural, but slightly larger; ar- 

 ticulates anteriorly with the posterior edge of the 

 urostyle, while posteriorly it supports the lower of the 

 middle two caudal fin rays. First hypural articulated 

 anteriorly with the posterior edge of the urostyle, while 

 posteriorly it supports three fin rays. The parhypural the 

 largest of the hypural series and enclosing the end of the 

 haemal canal with its deeply concave anterior end; the 

 lateral edges of its concave anterior end articulate by 

 fibrous tissue with the posterolateral surfaces of the cen- 

 trum. A slight indentation on the anterodorsal edge of 

 the parhypural marks the end of the haemal canal. The 

 parhypural is thus the not greatly modified haemal arch 

 and spine of the last vertebra. 



Caudal fin rays. — Twelve in number; the upper- 

 most ray and the lowermost ray unbranched, the others 

 becoming increasingly branched toward the two middle 

 fin rays, which are branched in triple dichotomies. The 

 fin rays articulate at their bifid bases by fibrous tissue 

 with the hypurals, as described above. 



DORSAL AND ANAL FINS. 



Dorsal Fin. 



Spines and pterygiophores. —Six spines borne on 

 five basal pterygiophores, without the intervention of 

 distal pterygial elements. The first spine long, the others 

 decreasing in length posteriorly in the series. First spine 

 with its generally concave base somewhat expanded ven- 

 trolaterally. The ventrolateral flanges of the first spine 

 are in close contact with one another medially, although 

 they are not fused together. Just above the basal area of 

 close apposition of the flanges, a hole is present antero- 

 posteriorly through the middle of the spine. The general- 

 ly concave basal surface of the spine fits over the general- 

 ly convex upper surface of the first pterygiophore, while 



at the same time a high medial flange from the upper 

 surface of the pterygiophore fits into the hole through the 

 base of the first spine. The medial flange of the pterygio- 

 phore possesses a large hole through which the two 

 medial surfaces of the base of the first spine come into 

 close fibrous tissue contact. The first spine is thus im- 

 possible to disarticulate from its pterygiophore without 

 cutting the fibrous tissue or breaking either the base of 

 the spine or the medial flange of its pterygiophore. The 

 first spine can be held in an erect position by a very sim- 

 ple mechanism. The ventral articular surface of the first 

 spine and the dorsal articular surface of the first 

 pterygiophore, on either side of its medial flange, are 

 rough and irregular. When the spine is erected at a right 

 angle to the dorsal surface of the pterygiophore and then 

 pulled slightly downward, a firm contact is established 

 between the two roughened articular surfaces and the 

 spine is effectively locked in position. The spine is un- 

 locked by relaxation of the strong, vertically directed 

 pressure of the spine against the pterygiophore, so that 

 the articular surface of the spine can slide forward over 

 the articular surface of the pterygiophore without undue 

 frictional resistance. The second spine articulates at its 

 concave ventral end with the generally convex surface of 

 the first pterygiophore directly behind the articular area 

 of the first spine, but the second spine has no function in 

 the locking mechanism of the first spine. There is a small 

 medial flange of the pterygiophore that fits loosely into 

 the slight concavity in the middle of the base of the sec- 

 ond spine. The third to the sixth spines articulate to 

 their individual basal pterygial elements and have, from 

 the third to sixth, progressively less concave articular 

 surfaces fitting against the progressively less convex ar- 

 ticular surfaces of their pterygiophores, so that the ar- 

 ticulation of the sixth spine to its pterygiophore is at the 

 relatively flat surfaces of both elements. 



The first basal pterygiophore has a strong antero- 

 ventrally directed columnar process which fits into a 

 groove formed by the intumed posteromedial surfaces of 

 the ventral half of the epiotics and the dorsal one-third of 

 the exoccipitals, as well as by the medial surfaces of the 

 bifid neural spine of the first vertebra, which overlies 

 these regions of the epiotics and exoccipitals. The colum- 

 nar portion of the first pterygiophore is held in this 

 groove by tough fibrous tissue. The second to fifth 

 pterygiophores bear, respectively, the third to sixth dor- 

 sal fin spines. The ventral regions of the second to fifth 

 pterygiophores articulate, respectively, between the 

 neural spines of the third and fourth vertebrae, the fifth 

 and sixth vertebrae, the sixth and seventh vertebrae, and 

 the seventh and eighth vertebrae. The pterygial elements 

 are cartilage filled at their extreme ventral edges. 



Fin rays and pterygiophores. — Sixteen fin rays 

 usually present; the first two rays and the last ray un- 

 branched, the others branched in single or double 

 dichotomies. Each fin ray has a small pair of distal 

 pterygiophores as two distinct halves between the bifur- 

 cate base of the ray, except for the last one or two rays, in 

 which these elements, if present, are unossified. Basally 



