posteromedially with the third basibranchial, while its 

 ventraily directed anterior end articulates by fibrous tis- 

 sue with the undersurface of the more anterior branchial 

 elements, although I am unable in the two study 

 specimens to see exactly where the attachments end. 

 Third ceratobranchial articulated ventraily with the 

 posterior end of the third hypobranchial and third 

 basibranchial, and dorsally with the third epibranchial. 

 Third epibranchial slender dorsally and somewhat ex- 

 panded ventraily; articulates dorsally with the third 

 pharyngobranchial. Third pharyngobranchial smaller 

 than the second pharyngobranchial but larger than the 

 fourth; bearing a single row of four or five long slender 

 teeth with relatively sharp points on the compressed 

 ventral edge of the bone; articulates ventraily with the 

 third epibranchial and is held by fibrous tissue more or 

 less closely to the second and fourth pharyngobranchials. 



Fourth arch. — Cerato-, epi-, and pharyngo- 

 branchial elements present. Fourth ceratobranchial ar- 

 ticulated ventraily with the cartilaginous area between 

 the third ceratobranchials and the third basibranchial, 

 and dorsally with the fourth epibranchial. Fourth epi- 

 branchial the longest of the epibranchial elements; rod- 

 like; articulates dorsally with the fourth pharyngo- 

 branchial. Fourth pharyngobranchial a very small plate 

 bearing a single row of two or three long slender teeth 

 much like those of the third pharyngobranchial but 

 slightly smaller. 



Fifth arch. — Ceratobranchial (lower pharyngeal) 

 element only. Fifth ceratobranchial the widest and 

 shortest of the ceratobranchial elements; much ex- 

 panded in the middle region of its length; articulates 

 ventraily with the cartilaginous region between the bases 

 of the fourth ceratobranchials; toothless. 



PAIRED FIN GIRDLES. 



Pectoral Fin. 



Posttemporal. —A large long shaft broadly over- 

 lying the lower half of the lateral surface of the pterotic, 

 to which it is firmly interdigitated; anterodorsally it also 

 interdigitates with the sphenotic, while its ventral head 

 is firmly held by fibrous tissue to the supracleithrum. On 

 its ventromedial surface the posttemporal helps, along 

 with the pterotic and, to a far lesser extent, the cleith- 

 rum, to support by fibrous tissue the expanded lateral 

 end of the ossified Baudelot's ligament. 



Baudelot's ligament. — This ligament is fully os- 

 sified as a large stout laterally expanded shaft giving 

 great support to the pectoral girdle. It interdigitates in 

 the midline with its opposite member and is firmly held 

 by fibrous tissue at its medial end to the ventral surface 

 of the parasphenoid just below the level of the origin of 

 the prootic shelf. Its expanded lateral end is firmly held 

 by fibrous tissue mainly to the ventromedial surface of 



the ventral flange of the pterotic and to the ventral end of 

 the posttemporal, and, to a much lesser extent, to the ex- 

 treme dorsal end of the cleithrum. Along its dorsal edge, 

 just lateral to its middle region, Baudelot's ligament con- 

 nects by fibrous tissue with the recurved portion of the 

 prootic shelf, while its ventral edge helps support by a 

 fibrous tissue sheet the dorsal edge of the medially ex- 

 panded platelike portion of the cleithrum. 



Supracleithrum. —Located slightly obliquely 

 posterodorsally to anteroventrally in relation to the axis 

 of the body; relatively short and overlain for a short dis- 

 tance anterodorsally by the ventral end of the posttem- 

 poral, to which it is articulated firmly and relatively im- 

 movably by fibrous tissue. The medial surface of the 

 supracleithrum broadly overlies and is firmly held by 

 fibrous tissue to the anterodorsal surface of the 

 cleithrum. 



Cleithrum. — Greatly expanded both laterally and 

 medially along all the length of its anterior edge, except 

 for a short distance ventraily, so that a large thin vertical 

 plate is formed at right angles to the axis of the body; 

 also greatly expanded posteriorly in the ventral two- 

 thirds of its length; articulates dorsally by fibrous tissue 

 on its lateral surface with the broadly overlying supra- 

 cleithrum and on its medial surface with the anterior end 

 of the dorsal postcleithrum; along its posterior edge it ar- 

 ticulates by fibrous tissue and interdigitation with the 

 anterior edge of the scapula, which it somewhat overlies 

 ventraily, while more ventraily along its posterior edge it 

 articulates through cartilage and slight interdigitation 

 with the coracoid. Ventromedially the cleithrum ar- 

 ticulates by fibrous tissue with its opposite member, 

 while the dorsal edge of its medially expanded platelike 

 portion is held by fibrous tissue to the ventral surface of 

 Baudelot's ligament. 



Postcleithra. — The postcleithra are greatly 

 expanded into an extremely wide, thin plate whose 

 lateral surface is closely held by fibrous tissue to the 

 cuirass. There are distinct dorsal and ventral segments, 

 the ventral segment much larger than the dorsal. The 

 anterior end of the dorsal segment articulates by fibrous 

 tissue with the medial surface of the dorsal end of the 

 cleithrum, while posteriorly it interdigitates with the 

 ventral postcleithrum. The ventral edges of both 

 postcleithra are thicker than the dorsal region, and the 

 anterior end of the dorsal postcleithrum is thickened and 

 shaftlike in the area of its articulation with the 

 cleithrum. 



Coracoid. — Somewhat wider ventraily than 

 dorsally; its posterior edge with a laterally directed 

 flange throughout its length, the flange ending dorsally 

 as a posteriorly directed prong below the lowermost ac- 

 tinost; cartilage filled at its dorsal and anterior edges; an 

 upraised flange present on its lower lateral surface, run- 

 ning, with increasing height of the flange, from postero- 



