fibrous tissue anterolaterally with the somewhat overly- 

 ing cleithrum and posteroventrally with the ventral 

 postcleithrum. The ventral postcleithrum is a slightly 

 compressed shaft which articulates by fibrous tissue 

 anterodorsally with the dorsal postcleithrum in the 

 region behind the pectoral fin rays. 



Coracoid. — Rounded dorsally, tapering ventrally to 

 a narrow shaft; produced posterodorsally into a prong 

 below the lowermost actinosts; cartilage filled along the 

 dorsal and anterior edges of its rounded dorsal region and 

 at the end of its ventral shaft; articulates by fibrous 

 tissue anterodorsally and anteroventrally with the 

 posterior surface of the cleithrum, dorsally through car- 

 tilage with the scapula and through fibrous tissue with 

 the bases of the last two actinosts. 



Scapula. — Completely encloses the scapular 

 foramen; cartilage filled at its anterior and ventral edges; 

 articulates anteriorly by fibrous tissue with the 

 cleithrum and ventrally through cartilage with the cor- 

 acoid. Posteriorly the scapula articulates by fibrous tis- 

 sue with the following elements, in order from dorsal to 

 ventral; the first pectoral fin ray, the small first actinost, 

 the second actinost, and the dorsal part of the base of the 

 third actinost. The first fin ray is supported on a stubby 

 projection, and the first actinost on a flattened surface 

 just posteroventral to the articulation of the first fin ray. 



the lateral edge of the pelvis, as well as ventrally with the 

 pelvis by an anteroventral flange from the base of the 

 spine, and dorsally with the pelvis by a smaller dor- 

 somedial flange (the anterior direction of the ventral 

 flange and the medial direction of the dorsal flange are 

 for the unerected spine). The spine can be envisioned to 

 lock in an erect position by a combination of three move- 

 ments. The whole spine is rotated approximately 70° 

 forward and outward around its base of articulation with 

 the pelvis. By this movement the ventral flange, that was 

 originally directed anteriorly, is now directed medially, 

 and the dorsal flange, that was originally directed 

 medially, is now pointed posteriorly and is no longer in 

 contact with the dorsal surface of the pelvis, but rather is 

 lying just lateral to the edge of the pelvis. The spine is 

 then slightly rotated so that the dorsal flange very slight- 

 ly overlies the ventrolateral edge of the pelvis. When the 

 spine is then rotated slightly backward and inward, the 

 dorsal flange hits flatly against the ventrolateral surface 

 of the pelvis and any further backward and inward move- 

 ment of the spine is stopped. The spine is unlocked by 

 the simple rotation of the spine slightly forward and out- 

 ward, and then slightly backward and upward, until the 

 dorsal flange is out of contact with the ventrolateral sur- 

 face of the pelvis and is lying just lateral to it. The spine 

 can then be drawn back to its unerected position, with 

 the dorsal flange sliding over the dorsal surface of the 

 pelvis to its original medially directed position. 



Actinosts. — Four elements; all cartilage filled at 

 both ends; the first two actinosts articulating with the 

 scapula, the third actinost articulating with the dorsal 

 edge of the region of articulation between the scapula 

 and coracoid, the fourth actinost articulating with the 

 coracoid; distally the actinosts support all of the pectoral 

 fin rays, except for the first. The actinosts increase in size 

 from the first to the fourth. 



Fin rays. — Thirteen fin rays in most specimens; 

 the first ray normal, of two equal halves, but only one- 

 fifth to one-fourth the length of the second ray and ar- 

 ticulating directly with the scapula rather than with the 

 actinosts, as do the other fin rays; the first two rays and 

 the last or lowermost ray unbranched, the intervening 

 rays branched. First ray without cross-striations; all 

 other rays with cross-striations. 



Pelvic fin. 



Pelvis.— Formed of two distinct lateral halves 

 tightly bound together medially by fibrous tissue; tapers 

 to a sharp point posteriorly, but terminates bluntly 

 anteriorly where it is tightly held by fibrous tissue 

 between the medial edges of the cleithra; expand- 

 ed ventrolaterally in the area anterior to the articulation 

 of the pelvic spines so that a large basin for muscle at- 

 tachment is formed on the ventral surface of the pelvis. 



Pelvic spine. — Large and strong; articulates 

 broadly by fibrous tissue at its concave medial edge with 



Fin rays. — Two rays present, only the first of which 

 can be seen externally. The first ray short, about one- 

 third the length of the spine, unbranched and without 

 cross-striations, the two halves of the ray distinct from 

 one another throughout their lengths and held together 

 by fibrous tissue. Basally the two halves of the first ray 

 are widely divergent, the base of the medial half of the 

 ray articulating broadly across the ventral surface of the 

 pelvis, while the base of the lateral half of the ray articu- 

 lates along the lateral surface of the pelvis. The second 

 fin ray is small and easily overlooked, for it lies flat 

 against the ventral surface of the pelvis and is completely 

 covered by the thick spinulose skin of the body. Like the 

 first ray, the second ray is composed of two distinct 

 halves that are held together by fibrous tissue. The 

 medial half of the second ray is wider than the lateral 

 half and both halves are unbranched and without cross- 

 striations. No pterygial elements are present. See Tyler 

 (1962b) for additional details on the pelvis and pelvic fin, 

 and Winterbottom (1970) for their muscular evolution. 



VERTEBRAL COLUMN. —All vertebrae with bi- 

 concave centra, except the last, which ends posterodor- 

 sally in the urostyle. 



Abdominal Vertebrae. 



First vertebra. —Neural spine enlarged, laterally 

 expanded dorsally, bifid to the centrum and hence 

 without a bony roof over the neural canal; articulates 

 over all of the anterior surface of its neural spine by 



