through cartilage and fibrous tissue. The branchial 

 arches are composed of three basibranchials, three pairs 

 of hypobranchials, five pairs of ceratobranchials, four 

 pairs of epibranchials, and three pairs of pharyngo- 

 branchials. Four gills are present, with a slit between the 

 fourth arch and the lower pharyngeal. 



branchial; about 12 to 15 teeth present in a single row, 

 the teeth like those of the outer series of the jaws, but 

 much smaller and with sharper points. The teeth 

 decrease in size posterolaterally in the series and are 

 replaced by new teeth developing in sockets below the 

 bases of the old teeth. 



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

 pharyngobranchial elements present. First basibranchial 

 short, wider posteriorly than anteriorly, displaced for- 

 ward so that it articulates posteriorly with the second 

 basibranchial and posterolaterally with the first hypo- 

 branchials. First hypobranchial very wide, more so 

 posterodorsally than ventrally; the largest of the hypo- 

 branchial elements, which decrease in size posteriorly in 

 the series; articulates ventrally with the region of ar- 

 ticulation between the first and second basibranchials 

 and dorsally with the first ceratobranchial. First cerato- 

 branchial a sturdy rod; the longest of the cerato- 

 branchial elements, which decrease in length posteriorly 

 in the series; no ventrally directed flange present on the 

 ceratobranchials, although from the second to the last 

 ceratobranchial the ventral ends of the elements become 

 increasingly enlarged; articulates dorsally with the first 

 epibranchial. First epibranchial with its ventral end 

 rounded and its dorsal end forming two divergent stubby 

 projections; its rounded ventral end articulates with the 

 first ceratobranchial, while the anterior projection of its 

 dorsal end articulates with the first pharyngobranchial, 

 and the posterior projection of its dorsal end with the 

 dorsal end of the second epibranchial and the ventral end 

 of the second pharyngobranchial. First pharyngo- 

 branchial (suspensory pharyngeal) short, slightly wider 

 ventrally than dorsally; articulates ventrally with the 

 first epibranchial and dorsally by fibrous tissue with the 

 ventral edge of the keel of the parasphenoid at the level 

 of the middle of the orbit. 



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

 pharyngobranchial elements present. Third basi- 

 branchial narrow anteriorly and posteriorly, but ex- 

 panded in the middle; articulates anteriorly with the sec- 

 ond basibranchial, anterolaterally with the second 

 hypobranchials, posterolaterally with the third hypo- 

 branchials, and posteriorly with the fourth cerato- 

 branchials. Third hypobranchial rounded posteriorly but 

 with a tapering anteroventral process that articulates by 

 fibrous tissue anteriorly with the ventral surface of the 

 more anterior basibranchials; articulates postero- 

 laterally with the third ceratobranchial and posteromedi- 

 ally with the posterior end of the third basibranchial. 

 Third ceratobranchial with a much expanded ventral 

 end; articulates ventrally with its opposite member 

 and with the third hypobranchial, and dorsally with 

 the third epibranchial. Third epibranchial a short rod 

 with a slightly expanded base and a short projection pos- 

 teriorly from the basal part of its posterior edge; ar- 

 ticulates dorsally with the third pharyngobranchial; the 

 projection from the basal portion of its posterior edge ar- 

 ticulates by fibrous tissue with a similar projection from 

 the anterior edge of the fourth epibranchial. Third 

 pharyngobranchial like the second pharyngobranchial, 

 except slightly smaller and with its ventral arm shorter 

 and wider; teeth in about the same number and arrange- 

 ment as described for the second pharyngobranchial; ar- 

 ticulates with the dorsal ends of the third and fourth epi- 

 branchials. The two toothed pharyngobranchial 

 elements are held to one another by fibrous tissue. 



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

 pharyngobranchial elements present. Second basi- 

 branchial longer than the first basibranchial and about 

 the same length as the third basibranchial, but wider 

 than either of the other two; articulates anteriorly with 

 the first basibranchial, anterolaterally with the first 

 hypobranchials, posteriorly with the third basibranchial 

 and posterolaterally with the second hypobranchials. Sec- 

 ond hypobranchial squarish, with a short posterior ex- 

 tension; articulates ventrally with the area of ar- 

 ticulation between the second and third basibranchial 

 and dorsally with the second ceratobranchial. Second 

 ceratobranchial a long rod with a slightly expanded ven- 

 tral end; articulates dorsally with the second epi- 

 branchial. Second epibranchial a short rod; articulates 

 dorsally with the second pharyngobranchial and the 

 posterodorsal arm of the first epibranchial. Second 

 pharyngobranchial with an elongate tooth bearing por- 

 tion and a short arm for articulation with the second epi- 

 branchial and the posterodorsal arm of the first epi- 



Fourth arch. — Cerato- and epibranchial elements 

 only. Fourth ceratobranchial much expanded ventrally; 

 articulates ventrally with the ventral end of its opposite 

 member and with that of the third ceratobranchial. 

 Fourth epibranchial rodlike; longer than the second and 

 third epibranchials; articulates ventrally with the fourth 

 ceratobranchial and dorsally with the base of the third 

 pharyngobranchial, and, from a short projection on its 

 lower anterior edge, with the third epibranchial. 



Fifth arch. — Ceratobranchial (lower pharyngeal) 

 element only. Fifth ceratobranchial the shortest of the 

 ceratobranchial elements; wider ventrally than dorsally, 

 with a short anterior projection from its anteroventral 

 edge; articulates ventrally with the base of the fourth 

 ceratobranchial; bearing two rows of teeth, the posterior 

 row much larger than the anterior row; teeth in both rows 

 similar to those of the pharyngobranchials, and becom- 

 ing smaller dorsally; about 25 teeth in the anterior row 

 and 15 in the posterior row. 



