normally tapering shaft, articulating with a slight inden- 

 tation on the ventromedial surface of the ceratohyal just 

 posterior to the articulation of the first branchiostegal. 

 The third to sixth branchiostegal rays articulate one just 

 behind the other with the lower half of the posterolateral 

 surface of the ceratohyal. The third branchiostegal is 

 more laterally expanded in the anterior third of its length 

 than are the other rays. 



Branchial Arches. — All the elements are cartilage 

 filled at their edges of articulation with the other 

 elements of the series, and the articulations are usually 

 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. Three gills are present; the fourth arch has no 

 gill and there is no slit between the fourth arch and the 

 lower pharyngeal. 



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

 pharyngobranchial elements present. First basi- 

 branchial the largest of the basibranchial elements; dis- 

 placed forward so that it articulates posteriorly with the 

 second basibranchial and posterolaterally with the first 

 hypobranchials. First hypobranchial the longest of the 

 hypobranchial elements; articulates ventrally with the 

 region of articulation between the first and second basi- 

 branchials and dorsally with the first ceratobranchial. 

 First ceratobranchial the shortest of the ceratobranchial 

 elements, which, except for the first ceratobranchial, in- 

 crease in length posteriorly in the series; possesses weak- 

 ly developed flanges from its anteroventral and postero- 

 ventral edges, similar flanges being increasingly well 

 developed on the second and third ceratobranchials but 

 not present on the fourth or fifth ceratobranchials; ar- 

 ticulates ventrally with the first hypobranchial and dor- 

 sally with the first epibranchial. First epibranchial a 

 slender rod; articulates dorsally with an upraised area on 

 the anterodorsal surface of the first pharyngobranchial. 

 First pharyngobranchial a relatively flat plate; wider 

 laterally than medially; bearing over all of its ventral 

 surface innumerable, small, villiform teeth, slightly 

 larger in the posterior region than anteriorly; articulates 

 at an upraised area on its anterodorsal surface with the 

 first epibranchial and at an upraised area on its postero- 

 dorsal surface with the second epibranchial. 



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

 pharyngobranchial elements present. Second basi- 

 branchial the smallest of the basibranchial elements; ar- 

 ticulates anteriorly with the first basibranchial, antero- 

 laterally with the first hypobranchials, posteriorly with 

 the third basibranchial, and posterolaterally with the 

 second hypobranchials. Second hypobranchial the short- 

 est of the hypobranchial elements; articulates ventrally 

 at the region of articulation between the second and third 

 basibranchials and dorsally with the second cerato- 

 branchial. Second ceratobranchial articulated dorsally 

 with the second epibranchial. Second epibranchial a long 



slender rod; like the first epibranchial, but with a slight 

 expansion on its posterior edge for fibrous tissue articu- 

 lation with the third epibranchial; articulates dorsally 

 principally to the upraised area on the second pharyngo- 

 branchial, only secondarily with the upraised area on the 

 posterodorsal surface of the first pharyngobranchial. Sec- 

 ond pharyngobranchial the longest of the pharyngo- 

 branchial elements; its toothed surface narrower but 

 longer than that of the first pharyngobranchial; in- 

 numerable villiform teeth present, like those on the first 

 pharyngobranchial, but with those along the posterior 

 edge distinctly larger than more anteriorly; articulates at 

 an upraised area on its dorsal surface principally with the 

 second epibranchial but also with the anterodorsal end of 

 the third epibranchial. 



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

 pharyngobranchial elements present. Third basi- 

 branchial somewhat wider posteriorly than anteriorly; 

 articulates anteriorly with the second basibranchial, 

 anterolaterally with the second hypobranchials, pos- 

 terolaterally with the third hypobranchials, and poste- 

 riorly with the fourth ceratobranchials. Third hypo- 

 branchial almost as long as the first hypobranchied; 

 directed anteroventrally under the second hypo- 

 branchial, with its narrow anterior end articulated by fi- 

 brous tissue with the region of the first basibranchial and 

 dorsal hypohyals. Third ceratobranchial articulated ven- 

 trally with the third hypobranchial and dorsally with the 

 third epibranchial. Third epibranchial thicker than 

 those anterior to it; expanded dorsally into two short 

 flanges, the more anterior of which articulates with the 

 upraised area on the second pharyngobranchial, while 

 the more posterior flange articulates with the anterior 

 edge of the fourth epibranchial. Third pharyngo- 

 branchial an elongate, thin, flat plate; toothless; held 

 in place primarily by fibrous tissue to the posterior 

 edge of the second pharyngobranchial, without any 

 special connection with any of the other branchial 

 elements. 



Fourth arch. —Cerato- and epibranchial elements 

 only. Fourth ceratobranchial a stout shaft; without ven- 

 tral flanges; the longest of the ceratobranchial elements; 

 articulates ventrally with the third basibranchial and 

 dorsally with the fourth epibranchial. Fourth epi- 

 branchial by far the longest and stoutest of the epi- 

 branchial elements; somewhat produced into a thin 

 flange posteriorly along the lower two-thirds of its length; 

 articulates ventrally with the fourth ceratobranchial, 

 while dorsally it ends in the general fibrous tissue that 

 binds the dorsal surfaces of the pharyngobranchial 

 elements to the ventral surfaces of the parasphenoid and 

 prootics. 



Fifth arch. —Ceratobranchial (lower pharyngeal) 

 element only. Fifth ceratobranchial large; slightly ex- 

 panded laterally along most of its length; toothless; ar- 

 ticulates ventrally with the base of the fourth cerato- 

 branchial. 



