PAIRED FIN GIRDLES. 



Pectoral Fin. 



Posttemporal. — A slender wedge of bone ventrally 

 where it is held in a deep concavity on the lateral surface 

 of the pterotic, but slightly expanded posterodorsally 

 where it contacts the sphenotic and, to a lesser extent, 

 the epiotic. It is firmly and immovably held to all three of 

 these bones, and especially to the pterotic, by a com- 

 bination of fibrous tissue and interdigitation. Ventrally 

 the posttemporal articulates by fibrous tissue with the 

 supracleithrum. 



Supracleithrum. — More or less vertical in position 

 in relation to the axis of the body; articulates im- 

 movably by fibrous tissue dorsally with the rounded ven- 

 tral head of the posttemporal and ventrally with the 

 cleithrum, which it broadly overlies. 



Cleithrum. — Laterally expanded at its anterior 

 edge, particularly in the middle one-third of its length; 

 articulates by fibrous tissue dorsally with the overlying 

 supracleithrum and with the dorsal postcleithrum, which 

 it overlies. Along its posterior edge the cleithrum broadly 

 overlies and articulates by fibrous tissue with the an- 

 terior edges of the scapula and coracoid. Ventromedially 

 the cleithrum articulates by fibrous tissue with its op- 

 posite member, and just above this region the anterior 

 end of the shaftlike pelvis is held between the cleithra. 



Postcleithra. — The postcleithra form a long 

 posteroventrally directed strut from the dorsomedial sur 

 face of the cleithrum along the abdominal wall muscula 

 ture to the area just above the dorsal lobe of the pelvis 

 The dorsal postcleithrum is wide anteriorly where it ar 

 ticulates by fibrous tissue with the overlying cleithrum 

 with a short dorsal projection from about the middle of 

 its length supporting the posteroventral edge of the en- 

 larged scales of the tympanum; tapering to a point pos- 

 teriorly where it broadly overlies and articulates by fi- 

 brous tissue with the anterodorsal region of the ventral 

 postcleithrum. The ventral postcleithrum a simple shaft, 

 tapering to a point posteriorly. 



Coracoid. — Wide dorsally, tapering to a blunt 

 point ventrally; with a short spinelike process under the 

 lowermost actinost from its posteroventral edge; the up- 

 per one-third of its posterior edge with an inturned flange 

 directed anteromedially, forming a broad basin for mus- 

 cle attachment; cartilage filled at its dorsal edge and for 

 a short distance at its anteroventral edge; articulates by 

 fibrous tissue anteriorly with the cleithrum, which 

 broadly overlies the dorsal one-half of its anterior edge; 

 articulates anterodorsally through cartilage and inter- 

 digitation with the scapula; articulates dorsally by fi- 

 brous tissue with the bases of the ventralmost two ac- 

 tinosts. 



Scapula. — Completely encloses the scapular 

 foramen; cartilage filled at its anterior and ventral edges; 

 articulates anteriorly and anteroventrally by fibrous tis- 

 sue with the overlying cleithrum; articulates postero- 

 ventrally through cartilage and interdigitation with the 

 coracoid. Along its posterodorsal edge the scapula ar- 

 ticulates by fibrous tissue with the following elements, in 

 order from anterodorsal to posteroventral: the first pec- 

 toral fin ray, the small first actinost, the second actinost, 

 and the anterior half of the base of the third actinost. 

 The articulations with the first pectoral fin ray and the 

 first actinost occur at upraised areas on the dorsal edge of 

 the scapula, the stubby projection supporting the first 

 pectoral fin ray being slightly larger than that sup- 

 porting the first actinost. 



Actinosts. — Four elements; all cartilage filled at 

 both ends; first actinost small, the others increasing 

 slightly in size posteroventrally in the series; first two ac- 

 tinosts articulated to the scapula as described in the 

 preceding section; third actinost articulated with the 

 dorsal edge of the articular area between the scapula and 

 coracoid and the fourth actinost with the coracoid; all 

 the articulations are by fibrous tissue. Distally the ac- 

 tinosts support by fibrous tissue all of the fin rays, ex- 

 cept for the first, which is supported by the scapula. 



Fin rays. — Fourteen fin rays in most specimens, 

 with the first ray about one-fifth the length of the second 

 ray and articulated directly with the scapula, rather than 

 with the actinosts, as are the other rays. First ray with its 

 medial half enlarged and thickened at its basal region of 

 articulation with the scapula; its lateral half reduced to a 

 thin, short splint closely held to the medial half, or even 

 fused to it. First two rays and the last ray unbranched, 

 the others branched. First ray without cross-striations, 

 all the other rays cross-striated. 



Pelvic Fin. 



Pelvis. — A stout shaft; not divided into separated 

 right and left halves; anterior half of its lateral surface 

 with a concavity for muscle attachment; a large dorsal 

 lobe present from its posterodorsal region which serves as 

 a place of tough fibrous tissue attachment for the over- 

 lying skin of the distensible abdominal area or ventral 

 flap (dewlap). A series of enlarged scales encircles the 

 posterior end of the pelvis and obscures from view the 

 rudimentary fin-ray (or spinous) element present in the 

 midline just behind the end of the pelvis. The lateral sur- 

 face of the posterior end of the pelvis bears several ridges 

 for articulation with these scales. The scales occur in four 

 segments, the anteriormost of which is immovably held 

 to the end of the pelvis, while the other three segments 

 are movable in a dorsoventral plane against the scales of 

 the first segment and the end of the pelvis. The fin-ray 

 element is deeply bifurcate anteriorly into divergent 

 dorsal and ventral halves, as described in detail by Tyler 

 (1962:228-229, figs. 30-37). The anterior one-third of the 



