sal region of the palatine. The posterior edge of the pos- 

 teromedial arm of the maxillary is supported against the 

 anterior vertical face of the ethmoid. The maxillary is 

 firmly interdigitated along most of its medial surface 

 with the premaxillary, except at the extreme ventral end 

 where it no longer overlies the premaxillary and articu- 

 lates by fibrous tissue with the lateral surface of the pos- 

 terodorsal end of the dentary. In the larger of the two 

 specimens the posteromedial arm of the premaxillary is 

 narrower and that of the maxillary wider than that illus- 

 trated for the smaller specimen, and the maxillary, 

 rather than the premaxillary, forms the major articu- 

 lation with the ethmoid and vomer. 



Lower Jaw. 



Dentary. — Dentaries indistinguishably fused 

 together at what would normally be their medial edges of 

 contact, so that the combined dentaries form a massive 

 U-shaped bone. No medial line of fusion between the two 

 halves can be observed externally or internally, but the 

 two canals leading into the pulp cavity occur side by side 

 to either side of the midline. The pulp cavity of the com- 

 bined dentaries is smaller than that of the premaxil- 

 laries. The teeth of the crushing jaw are exactly like those 

 described for the premaxillary, as are those of the tri- 

 turation plate, and are formed from primordia in the 

 same way. The trituration plate of the dentaries, 

 however, is a single, almost squarish, massive block 

 which shows no evidence of the fusion line between what 

 may be assumed to have been at one time the separate 

 right and left halves. The posterior end of the dentary is 

 extremely concave to accommodate the articular, to 

 which it attaches by interdigitation. Posteroventrally the 

 dentary articulates by fibrous tissue with the angular. 

 The dorsolateral surface of the dentary articulates by fi- 

 brous tissue with the ventromedial surface of the max- 

 illary. 



Articular. — More or less triangular in shape; its 

 posterior edge somewhat laterally expanded; cartilage 

 filled at its anterior edge where it is continuous with the 

 remains of Meckel's cartilage; articulates by interdigi- 

 tation over most of its lateral surface and over the ante- 

 rior portions of its medial surface with the dentary. 

 Posteroventrally it interdigitates with the angular. At 

 the concave surface of the lateral expansion on its lower 

 posterior edge the articulfir is supported through fibrous 

 tissue by the anterior knob of the quadrate. The sesa- 

 moid articular is a slightly elongate nubbin of bone held 

 alongside the anteromedial edge of the articular just 

 above the remains of Meckel's cartilage and just below 

 the posteromedial edge of the dentary, and is relatively 

 much larger in the larger specimen than in the small- 



Angular. — Small; articulates dorsally by inter- 

 digitation with the articular and anteriorly by fibrous tis- 

 sue with the dentary. Posteriorly it connects by ligament 

 with the anterior end of the interoperculum. 



BRANCHIAL APPARATUS. 



Hyoid Arch, Branchiostegal Rays, and Urohyal. 

 Hypohyals. — Both hypohyal elements present, the 

 dorsal the larger of the two; dorsal hypohyal cartilage fill- 

 ed at its posterior and ventral edges, ventral hypohyal 

 cartilage filled at its posterior and dorsal edges; both 

 hypohyals articulate through cartilage and, in the larger 

 of the two specimens, by slight interdigitation of their 

 medial edges with one another and with the ceratohyal; 

 dorsomedially the dorsal hypohyal articulates by fibrous 

 tissue with its opposite member. 



Ceratohyal. — Elongate; dorsoventrally expanded 

 at both its anterior and posterior ends; cartilage filled at 

 its anterior and posterior edges; articulates through car- 

 tilage anteriorly with the dorsal and ventral hypohyals 

 and posteriorly with the epihyal, strengthened in the 

 case of the larger of the two specimens by slight inter- 

 digitation. Of the six branchiostegal rays, the first three 

 are held directly to the ceratohyal and the fourth is held 

 near the posterior edge of the ceratohyal on the cartilage 

 separating the latter from the epihyal. The somewhat 

 enlarged first branchiostegal ray is held to the lower 

 lateral surface of the ceratohyal about one-third the way 

 back its length. The second branchiostegal ray is held to 

 a very slight concavity in about the middle of the ventral 

 edge of the ceratohyal or slightly dorsomedial to it, while 

 the third branchiostegal attaches to the lower postero- 

 lateral surface of the ceratohyal. 



Epihyal. — Rounded posteroventrally but slightly 

 prolonged anterodorsally; cartilage filled at its ventral 

 and anterior edges; articulates through cartilage and, in 

 the larger specimen, by interdigitation anteriorly with 

 the ceratohyal, while at a slight prominence on its pos- 

 terodorsal edge it articulates by fibrous tissue with the 

 interhyal. Just below its articulation with the interhyal, 

 the epihyal articulates by fibrous tissue laterally with the 

 interoperculum. 



Interhyal. — An elongate column; 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 hyomandibular, metaptery- 

 goid, symplectic, and preoperculum. 



Branchiostegal rays. — Six in number; the first 

 branchiostegal ray shorter but, in the anterior two-thirds 

 of its length, wider than the other rays; its dorsal edge 

 distinctly curved medially while its ventral platelike ex- 

 pansion lies in the vertical plane; articulates by fibrous 

 tissue with the lower lateral surface of the ceratohyal 

 about one-third the way back its length. The second 

 branchiostegal ray is a long thin shaft held to about the 

 middle of the length of the ventral edge of the ceratohyal 

 in the smaller specimen (illustrated), but distinctly on 

 the medial surface just above the middle of the ventral 

 edge in the larger specimen. The third and fourth 

 branchiostegal rays are slightly shorter, and much 

 stouter anteriorly, than the second ray. The third ray is 



