134 ALUS. [Vol. XVIII. 



face of the bone is deeply hollowed, near the middle of its superior 

 edge, and there gives insertion to the anterior division of the in- 

 ternal levator of the arches, and to the obliquus dorsalis of the 

 first arch. The inferior, or postero-mesial surface of the bone 

 is deeply hollowed in its anterior half, and the dorsal edge of the 

 bone, above the hollow, gives insertion to parts of the obliquus 

 dorsalis of the second arch, and of the transversus dorsalis an- 

 terior. The inferior surface of the bone, behind the depression, 

 is overlapped mesially by the anterior pointed end of the third 

 infrapharyngobranchial. 



The dorsal edge of the anterior portion of the element is carti- 

 laginous, the cartilage extending backward to about the middle 

 point of the dorsal edge of the element, where it ends, presenting 

 a free hind end which gives articulation to the proximal end of 

 the suprapharyngobranchial of the first arch. This cartilaginous 

 edge of the infrapharyngobranchial lies parallel to and ventro- 

 postero-mesial to the anterior end of the first epibranchial ; and 

 the anterior ends of the two elements are bound together by 

 fibrous tissues. 



At about the middle of the posterior half of the dorsal edge of 

 the infrapharyngobranchial, and immediately posterior to the de- 

 pressed region on its inferior surface, there is another piece of 

 cartilage, the outer surface of which is presented backward, dor- 

 sally and laterally. It gives articulation to the anterior part of 

 the proximal articular head of the second epibranchial. 



The Third and Fourth Infrapharyngobranchial {IPB 

 III-IV) are firmly united to form the posterior and larger o-f the 

 two superior pharyngeal bones of each side of the head. The two 

 elements are however not fused, and can be easily separated with- 

 out fracture. Both bones have a large dermal portion which 

 covers their ventral surfaces and bears the bristles with which 

 the bones are furnished. Both bones are strongly convex on their 

 ventral surfaces, and their bristles form a large, longitudinal, con- 

 vex pad on the dorsal surface of the branchial cavity. The 

 pads of opposite side of the head are separated from each other 

 by a deep, wide, median groove. The postero-lateral ends of the 

 anterior pharyngeal pads touch the lateral edges of the anterior 

 ends of the posterior pads, and, from there, run forward and 



