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

 pharyngobranchial elements present. Second basi- 

 branchial short, but much expanded laterally both 

 anteriorly and posteriorly; articulates anteriorly with the 

 first basibranchial, posteriorly with the third basi- 

 branchial, anterolaterally with the first hypobranchials, 

 and posterolaterally with the second hypobranchials. 

 Second hypobranchial a short rod; articulates ventrally 

 with the posterolateral surface of the second basi- 

 branchial and dorsally with the second ceratobranchial, 

 which in turn articulates dorsally with the second 

 epibranchial. Second epibranchial a slender rod; articu- 

 lates dorsally with the ventral arm of the second 

 pharyngobranchial. Second pharyngobranchial roughly 

 L-shaped; bearing a single row of 12 to 17 well-de- 

 veloped teeth, which are relatively sharp pointed and 

 curved slightly posteriorly, along the larger of the two 

 wings of the L. The toothless ventral wing articulates 

 principally with the second epibranchial, but also, to a 

 lesser extent, with the third epibranchial. The teeth are 

 set in shallow sockets and are replaced by new teeth de- 

 veloping in sockets just anterior to and below the bases of 

 the old teeth. The second pharyngobranchial is held to 

 the other two pharyngobranchial elements by fibrous tis- 



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

 ryngobranchial elements present. Third basibranchial 

 like second basibranchial, but larger; articulates 

 anteriorly with the second basibranchial, posteriorly 

 with the fourth ceratobranchials and posterolaterally 

 with the third hypobranchials. Third hypobranchial with 

 an anteroventral process that articulates by fibrous 

 tissue with the ventral surface of the first basibranchial; 

 posteriorly it articulates with the posterolateral surface 

 of the third basibranchial and with the ventral edge of 

 the third ceratobranchial. Third ceratobranchial articu- 

 lated ventrally with the third hypobranchial and dorsally 

 with the third epibranchial. Third epibranchial a stout 

 rod, with a stubby projection from its posterolateral sur- 

 face articulating by fibrous tissue with a similar process 

 from the fourth epibranchial; articulates dorsally with 

 the second and third pharyngobranchials. Third pharyn- 

 gobranchial roughly L-shaped, with the larger of the two 

 arms bearing about 10 to 12 teeth in a single row; teeth 

 similar to those of the second pharyngobranchial and 

 replaced in a similar manner; articulates by the smaller 

 of its two arms ventrally with the third and fourth 

 epibranchials. 



Fourth arch. — Cerato- and epibranchial elements 

 only. Fourth ceratobranchial the longest of the cerato- 

 branchial elements; articulates ventrally with the third 

 basibranchial and dorsally with the fourth epibranchial. 

 Fourth epibranchial an elongate rod, the longest of the 

 epibranchial elements; possesses a stubby projection 

 from its anterolateral edge which articulates through 

 fibrous tissue with the similar process on the third 

 epibranchial; articulates dorsally with the third 

 pharyngobranchial. 



Fifth arch. —Ceratobranchial (lower pharyngeal) 

 element only. Fifth ceratobranchial a stout rod, slightly 

 expanded medially in about the first one-third of its 

 length; toothless; articulates ventrally with the base of 

 the fourth ceratobranchial. 



PAIRED FIN GIRDLES. 



Pectoral Fin. 



Supracleithrum. —In position at about a 45° angle 

 to the axis of the body; a stout shaft with a lateral flange 

 along most of its length; articulates by fibrous tissue dor- 

 sally with a slight concavity on the posterior surface of 

 the pterotic and ventrally with the cleithrum, which it 

 overlies. 



Cleithrum. — Laterally expanded along most of its 

 length; articulates by fibrous tissue dorsally with the 

 overlying supracleithrum and with the dorsal post- 

 cleithrum, which it overlies. Along its posterior surface it 

 articulates by fibrous tissue with the scapula and cora- 

 coid. Ventromedially the cleithrum articulates by tough 

 fibrous tissue with its opposite member in the midline of 

 the body between the medial edges of the horizontal 

 platelike portions of the first branchiostegal rays. 



Postcleithra. — The postcleithra form a long strut, 

 widened posteriorly, along the abdominal wall muscula- 

 ture from the supracleithrum to about halfway back the 

 length of the abdominal cavity. The dorsal postcleithrum 

 articulates by fibrous tissue anterolaterally with the 

 overlying cleithrum and posterolaterally with the ventral 

 postcleithrum, which is much deeper and more laterally 

 compressed than the dorsal postcleithrum. 



Coracoid. — Rounded dorsally, but tapering to a 

 point anteroventrally; a posterodorsally directed spine- 

 like process present from its posteroventral edge; carti- 

 lage filled at its dorsal edge; articulates anteriorly by 

 fibrous tissue with the cleithrum and dorsally through 

 cartilage with the scapula and the second to fourth ac- 

 tinosts. 



Scapula. — Scapular foramen not entirely enclosed 

 by the scapula, but, rather, with its anterior edge closed 

 by the cleithrum; cartilage filled at its dorsal, ventral, 

 and anterior edges; articulates by fibrous tissue anterior- 

 ly with the cleithrum, posteriorly by slight interdigi- 

 tation dorsally with the small first actinost and ventrally 

 with the base of the second actinost, and through carti- 

 lage ventrally with the coracoid. 



Actinosts. — Four elements; all cartilage filled at 

 both ends, except for the first, which is only cartilage fill- 

 ed at its dorsal edge. The first actinost is reduced to a 

 small wedge between the upper regions of the scapula 

 and the second actinost, articulating with the former by 

 interdigitation and with the latter through cartilage. The 

 second and third actinosts are constricted in the middle, 



271 



