hyal but then diverging into two prongs; the anterior 

 prong articulates by fibrous tissue with the ventral 

 keel of the parasphenoid just anterior to the middle of 

 the orbit, while the posterior prong articulates with 

 the anteriormost pharyngobranchial (that of the second 

 arch) and the dorsal end of the second epibranchial. The 

 pharyngobranchial element of the first arch is absent. 



Second arch. — Basi-, hypo-, cerato-, epi-, and 

 pharyngobranchial elements present. Second basi- 

 branchial the longest of the three elements of the series 

 and slightly wider posteriorly than anteriorly; articu- 

 lates anteriorly with the first basibranchial, antero- 

 laterally with the first hypobranchials, posteriorly with 

 the third basibranchial, and posterolaterally with the 

 second hypobranchials. Second hypobranchial wider 

 posterodorsally than anteroventrally; articulates ventral- 

 ly with the area of articulation between the second and 

 third basibranchials and dorsally with the second cerate- 

 branchial. Second ceratobranchial a long rod with a 

 slightly expanded ventral end; articulates dorsally with 

 the second epibranchial. Second epibranchial a short 

 rod; articulates dorsally with the second pharyngo- 

 branchial and, to a lesser extent, with the posterodorsal 

 arm of the first epibranchial. Second pharyngobranchial 

 (the first of the two remaining elements of the series) an 

 oblong block bearing on its ventral surface a row of about 

 five slender sharply pointed teeth and articulating ven- 

 trally with the dorsal end of the second epibranchial and 

 the posterodorsal projection of the first epibranchial. 

 New teeth develop in sockets just behind and below the 

 bases of the old teeth. 



Third arch. — Basi-, hypo-, cerato-, epi-, and 

 pharyngobranchial elements present. Third basibran- 

 chial a short column, widest in the middle; articulates 

 anteriorly with the second basibranchial, anterolaterally 

 with the second hypobranchials, posterolaterally with 

 the third hypobranchials, and posteriorly with the 

 fourth ceratobranchials. Third hypobranchial rounded 

 posteriorly but with a short tapering anteroventral 

 process that articulates by fibrous tissue anteriorly 

 with the ventral surface of the more anterior basi- 

 branchials and the posterior arm of the urohyal; arti- 

 culates posterolaterally with the third ceratobranchial 

 and posteromedially with the posterior end of the third 

 basibranchial. Third ceratobranchial expanded ventrally 

 but shaftlike more distally; articulates ventrally with its 

 opposite member and with the third hypobranchial, and 

 dorsally with the third epibranchial. Third epibranchial 

 rodlike distally and expanded in the middle region; ar- 

 ticulates dorsally with the third pharjoigobranchial; the 

 expanded middle region is directed anteriorly and ar- 

 ticulates with the basal region of the second 

 epibranchial. Third pharyngobranchial like the second 

 pharyngobranchial except smaller and usually with only 

 three teeth, the teeth slightly smaller than those of the 

 other pharyngobranchial; articulates ventrally with the 

 distal ends of the third and fourth epibranchials. The two 



pharyngobranchial elements are held to one another by 

 fibrous tissue. 



Fourth arch. — Cerato- and epibranchial elements 

 only. Fourth ceratobranchial more compressed than the 

 other ceratobranchials and with a narrow ventral flange; 

 articulates ventrally with the ventral end of its opposite 

 member and that of the third ceratobranchial. Fourth 

 epibranchial rodlike, only slightly larger in the middle 

 than at either end; articulates ventrally with the fourth 

 ceratobranchial and dorsally with the third pharyngo- 

 branchial. 



Fifth arch. — Ceratobranchial (lower pharyngeal) 

 element only. Fifth ceratobranchial the shortest of the 

 ceratobranchial elements; ntirrowest dorsally, widest in 

 the middle, and with an expanded base articulating with 

 the base of the fourth ceratobranchial; toothless. 



PAIRED FIN GIRDLES. 



Pectoral Fin. 



Posttemporal. — A short relatively straight shaft 

 broadly overlying the lateral surface of the pterotic and, 

 to a lesser extent, the sphenotic and extensively inter- 

 digitated to both, and therefore immovably held to the 

 skull; articulates ventrally through fibrous tissue with 

 the dorsal head of the supracleithrum. 



Supracleithrum. — A straight shaft of bone oriented 

 more or less vertically to the axis of the body; most of its 

 medial surface broadly overlying and held by fibrous 

 tissue to the lateral surface of the upper end of the 

 cleithrum, while dorsally it articulates immovably 

 through fibrous tissue with the head of the posttemporal. 



Cleithrum. — Laterally expanded at its anterior 

 edge in the middle of its length; articulates by fibrous 

 tissue dorsally with the overlying supracleithrum and 

 with the upper end of the postcleithrum, which it broadly 

 overlies. Along its posterior edge the cleithrum overlies 

 the anterior region of the scapula and coracoid and ar- 

 ticulates with both through fibrous tissue and slight in- 

 terdigitation. Along the ventral two-thirds of its length 

 the medial edges of the two cleithra are firmly held to one 

 another by fibrous tissue, while ventromedially they also 

 articulate through strong fibrous tissue with the anterior 

 end of the shaftlike portion of the pelvis which is closely 

 held between the two cleithra. 



Postcleithrum. — The postcleithrum is a long 

 flattened strong strut not divided into dorsal and ventral 

 parts. The dorsal end of the postcleithrum articulates by 

 fibrous tissue with the dorsomedial surface of the cleith- 

 rum. The postcleithrum is angled obliquely down from 

 its upper point of attachment toward the region of 

 the abdominal wall in front of the dorsal lobe of the 

 pelvis. 



