right and left halves, each of which contains four or five 

 elongate teeth. The teeth are set in deep sockets and re- 

 main distinct and separate from one another but become 

 increasingly intimately held to the bony matrix ante- 

 riorly. As an old tooth at the anterior end of the tritura- 

 tion plate is worn away or resorbed, a new tooth devel- 

 ops in a new socket at the posterior end of the plate. In 

 the two sets of jaws from specimens apparently at least 

 several times as large as the two cleared and stained 

 specimens, the teeth of the trituration plate are far more 

 numerous, less regularly arranged, relatively smaller and 

 placed more anteriorly on the undersurface of the pre- 

 maxillaries. The trituration teeth apparently undergo ex- 

 tensive change with increasing size. 



Maxillary. —Straight and rather flattened, except 

 dorsally where it becomes expanded into a large rounded 

 head which fits into the deep concavity on the dorsal sur- 

 face of the premaxillary. Below the latter region the max- 

 illary broadly overlies and articulates by fibrous tissue 

 with the dorsal surface of the premaxillary. Posterodor- 

 sally the medial ends of the two maxillaries and the 

 medial edge of the fused premaxillaries articulate by a 

 fibrous tissue sheet with the anterior edges of the eth- 

 moid and vomer. The ventromedial surface of the maxil- 

 lary articulates by fibrous tissue with the dorsolateral 

 surface of the dentary. 



medial surface of the dentary. Posteroventrally the 

 medial surface of the articular is concave and forms a 

 groove in which the dorsal end of the angular is held by 

 fibrous tissue. In about the middle of its posterior edge 

 the articular possesses a transverse groove which articu- 

 lates by fibrous tissue with the quadrate. A sesamoid ar- 

 ticular is absent. 



Angular. — A short rod; cartilage filled at its dorsal 

 edge; articulates by fibi-ous tissue anteriorly with the 

 dentary and dorsally with the groove on the medial sur- 

 face of the articular. Posteriorly the angular connects 

 with the ligament that encloses the interoperculum. 



BRANCHIAL APPARATUS. 



Hyoid Arch and Branchiostegal Rays. 



Hypohyals. — Dorsal and ventral hypohyals 

 present, the ventral slightly larger than the dorsal; the 

 ventral and posterior edges of the dorsal hypohyal and 

 the dorsal and posterior edges of the ventral hypohyal 

 cartilage filled; articulate through cartilage with one 

 another and with the anterior edge of the ceratohyal. The 

 anterodorsal end of the dorsal hypohyal articulates by 

 fibrous tissue with the middle of the lateral surface of the 

 basibranchial. The anteromedial edges of the hypohyals 

 articulate by fibrous tissue with their opposite members. 



Dentary. — The two dentaries are indistinguish- 

 ably fused in the midline and, with the fused teeth, form 

 a large nibbling plate like that of the upper jaw. The pos- 

 teromedial surfaces of the fused dentaries are deeply con- 

 cave to receive and articulate by fibrous tissue with the 

 anterior ends of the articulars. Posteroventrally the den- 

 tary articulates by fibrous tissue with the anterior end of 

 the angular. Posterodorsally along its lateral surface the 

 dentary articulates by fibrous tissue with the medial sur- 

 face of the maxillary. The biting edge of the dentary is a 

 hard and apparently completely homogenous substance, 

 like that of the upper jaw. A trituration plate composed 

 of separate, but closely apposed, right and left halves is 

 present on the medial third of the inner surface of the 

 fused dentaries in the two relatively small cleared and 

 stained specimens. Each side contains two series of 

 separate and distinct teeth set in deep sockets. The inner 

 series contains four elongate teeth, while the other series 

 contains three somewhat rounded teeth. The pulp cav- 

 ity and replacement of the teeth of the trituration plate 

 are the same as described for the fused premaxillaries, 

 and the two sets of jaws from much larger specimens sim- 

 ilarly have far more numerous and smaller teeth placed 

 more anteriorly on the bone. 



Articular. — More or less triangular in shape; car- 

 tilage filled for a short distance anteriorly on its medial 

 surface where it is continuous with the remains of 

 Meckel's cartilage. The tapering anterior portion of the 

 articular articulates by fibrous tissue with the concave 



Ceratohyal. — Short, but wide; more expanded 

 anteriorly than posteriorly; cartilage filled at its anterior 

 knd posterior edges; articulates through cartilage ante- 

 riorly with the hypohyals and posterodorsally with the 

 epihyal. The posterior half of the ventral edge of the cera- 

 tohyal possesses two successive indentations separated 

 by a ventrally directed prong. The ceratohyal supports 

 the first three branchiostegal rays. 



Epihyal.— Small; cartilage filled along its anterior 

 and ventral edges; articulates anteriorly and ventrally 

 through cartilage with the ceratohyal, while posterodor- 

 sally it articulates by fibrous tissue with the base of the 

 interhyal, and laterally supports the last few branchios- 

 tegal rays. The lateral surface of the epihyal articulates 

 by fibrous tissue with the ligament enclosing the inter- 

 operculum at the level of the posterior end of the latter. 



Interhyal. — A short, thick column; deeply carti- 

 lage filled at both ends; articulates by fibrous tissue ven- 

 trally with the epihyal and dorsally with the cartilagi- 

 nous area between the hyomandibular, ectopterygoid, 

 sympletic, and preoperculum. 



Branchiostegal rays. —Six in number; the first five 

 rays long, flat, and relatively straight; the sixth branchi- 

 ostegal wide for a short distance anteriorly, but rapidly 

 tapering posteriorly to a long, thin, slender shaft. The 

 branchiostegal rays articulate by fibrous tissue with the 

 hyoid arch elements as follows: first and second branchi- 

 ostegals with the successive concavities on the ventral 



