stubby trituration teeth as there are on the ventral sur- 

 face of the premaxillary. Ventromedially the dentary ar- 

 ticulates by fibrous tissue with its opposite member, with 

 about 15 stubby projections strengthening the articu- 

 lation, as in the case of the premaxillary. 



Articular. — More or less triangular in shape, with 

 the apex pointing anteriorly into the hollowed out pos- 

 terior part of the dentary; cartilage filled at its anterior 

 edge where it is continuous with the remains of Meckel's 

 cartilage; articulates by fibrous tissue and interdigi- 

 tation anteriorly with the dentary, posteriorly by fibrous 

 tissue at a groove on its surface with the knoblike 

 anterior end of the quadrate, posteroventrally by fibrous 

 tissue, and interdigitation in large specimens, with the 

 angular. The sesamoid articular is a rod of bone lying 

 alongside the anteromedial surface of the articular just 

 posterior to the region where the latter interdigitates 

 with the dentary. 



Angular. — Small; articulates by fibrous tissue with 

 the dentary and articular, or in large specimens by inter- 

 digitation with both of these bones. Posteriorly the angu- 

 lar makes ligamentous connection with the anterior end 

 of the interoperculum. 



BRANCHIAL APPARATUS. 



Hyoid Arch and Branchiostegal Rays. 



Hypohyals. — Both hypohyal elements present but 

 not large, the dorsal hypohyal being particulfirly small; 

 dorsal hypohyal cartilage filled at its ventral edge and 

 ventral hypohyal cartilage filed at its posterior edge. The 

 hypohyals articulate through cartilage with one another 

 and with the ceratohyal, while they articulate by fibrous 

 tissue anteromedially with their opposite members. 



Ceratohyal. — Elongate, somewhat expanded pos- 

 teriorly; cartilage filled at its anterior and posterior 

 edges; articulates through cartilage anteriorly with the 

 hypohyals and through cartilage and interdigitation 

 posterodorsally with the epihyal. Of the six branchios- 

 tegal rays, only five usually articulate by direct contact 

 through fibrous tissue with the ceratohyal. 



Epihyal. — Rounded posteriorly; cartilage filled at 

 its anterior edge; articulates anteriorly through cartilage 

 and interdigitation with the ceratohyal and by fibrous 

 tissue posterodorsally with the interhyal and laterally 

 with the ventral flange of the interoperculum. 



Interhyal. — Short and columnar; cartilage filled at 

 its dorsal and ventral edges; articulates by fibrous tissue 

 ventrally with the epihyal and dorsally with the fibrous 

 tissue sheet between the symplectic, metapterygoid, and 

 preoperculum. 



Branchiostegal rays. — Six in number; the first 

 branchiostegal ray a large, relatively flat horizontal plate 



with a down -turned lateral edge which anteriorly be- 

 comes a thick vertical flange for articulation by fibrous 

 tissue with a vertical groove in the middle of the medial 

 surface of the ceratohyal. The second branchiostegal ray 

 is the longest of the six elements and it is a normal unex- 

 panded shaft articulating by fibrous tissue with the ven- 

 tral edge of the ceratohyal just posterior to the region of 

 articulation of the first branchiostegal ray. The third, 

 fourth, and fifth branchiostegal rays are also normal in 

 shape, increasing slightly in length from the third to fifth 

 and articulating by fibrous tissue with the lateral sur- 

 face of the posteroventral region of the ceratohyal. The 

 sixth branchiostegal ray is sometimes broad posteriorly, 

 but always tapers to a narrow shaft anteriorly where it 

 articulates by fibrous tissue with the dorsal edge of the 

 fifth branchiostegal ray, rather than with the cera- 

 tohyal. 



Branchial Arches. — All the elements are cartilage 

 filled at their edges of articulation with the other ele- 

 ments of the series, and the articulations are usually 

 mediated through cartilage and fibrous tissue. The bran- 

 chial 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 pos- 

 sesses no gill and there is no slit between it and the lower 

 pharyngeal. 



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

 pharyngobranchial elements present. First basi- 

 branchial elongate and rodlike; displaced forward so that 

 it articulates posteriorly with the second basibranchial 

 and posterolaterally with the first hypobranchials. First 

 hypobranchial slightly expanded dorsally; the largest of 

 the hypobranchial elements, which decrease in size pos- 

 teriorly in the series; articulates ventrally with the re- 

 gion of articulation of the first basibranchial with the 

 second basibranchial and dorsally with the first cera- 

 tobranchial. First ceratobranchial the shortest of the 

 ceratobranchial elements, which, except for the fifth 

 ceratobranchial, increase in size posteriorly in the series; 

 possesses a ventrally directed flange along most of its 

 ventral surface, this flange on the succeeding cera- 

 tobranchials decreases in size posteriorly until it is al- 

 most absent on the last ceratobranchial; articulates dor- 

 sally with the first epibranchial. First epibranchial a nar- 

 row rod; the shortest of the epibranchial elements, which 

 increase in length posteriorly in the series; articulates 

 dorsally with the first pharyngobranchial. First pharyn- 

 gobranchial (suspensory pharyngeal) a rounded plate 

 with a short ventral process for articulation with the first 

 epibranchial; toothless; placed in line with the two tooth 

 bearing pharyngobranchials rather than being oriented 

 toward, and having its distal end attached by fibrous 

 tissue to, the ventral surface of the skull. The dorsal re- 

 gions of the branchial arches are held to the ventral sur- 

 faces of the parasphenoid and prootics by fibrous tissue 

 attaching to the dorsolateral surfaces of the epibran- 

 chials and pharyngobranchials. 



