Remains of the Pycnodont Fish, Mesturus. 7 



base of the skull (PI. III. figs. 4, 4 a) is also interesting. It 

 is bilaterally symmetrical and seems to have been formed in 

 cartilage; and the only suggestion the present writer can 

 make is that it represents a basisphenoid immediately behind 

 the parasphenoid. It is longer than broad, and its presumably 

 inferior face (fig. 4) exhibits a longitudinal keel which is 

 partly broken away ; it is narrowest at what appears to be its 

 hinder extremity, while the lateral margins form sharp edges, 

 each apparently notched near its anterior end. There is an 

 oblique roughened articular surface behind, shown on the 

 lower aspect (fig. 4, p-f.), and another similar surface, sloped 

 in the opposite way, appears from the inferior aspect in front 

 (a./.), this fitting very well upon the parasphenoid if it 

 happens to have been placed as here supposed. The inner 

 face of this problematical bone (fig. 4 a) is comparatively 

 flat, exhibiting only a possible articular surface at its narrowed 

 posterior end. A pair of large foramina pierce the bone 

 obliquely near its middle, the inferior opening being situated 

 further forwards than its superior exit. 



Jaws and Facial Bones. 



The mandibular suspensorium is unknown and the pterygo- 

 quadrate arcade is exhibited only in one specimen (no. 1). 

 Like that of Anomceodus Willeti, this arcade is in the form 

 of a delicate toothless plate (PI. I. fig. 1, ptq.), but it is un- 

 fortunately only preserved and exposed in its most posterior 

 portion, where the concavely arched front margin of the ecto- 

 pterygoid passes into that of the quadrate {qu.). The latter 

 element is comparatively robust, and it seems to exhibit a 

 surface of attachment for the symplectic along nearly the 

 whole of its hinder margin ; at least an apparently articular 

 surface may be observed in this position on both sides of the 

 only known specimen. Its articular face for the mandible is 

 irregularly oval, much deeper than broad, and slightly con- 

 cave. The premaxillaB {pmx.) are robust, deep, and narrow, 

 meeting in the middle line and each showing the bases of 

 three teeth. They are smooth and overlapped by the tuber- 

 culated ethmoidal plates, and each is notched on its outer 

 lateral margin. Whether or not any facial element can be 

 identified with the maxilla is uncertain ; but one large tuber- 

 culated cheek-plate (?/), deeper behind than in front, extends 

 down to the border of the upper jaw. This plate is very 

 thin and toothless. A small ciieek-plate (z) covers the outer 

 face of the postfrontal bone, and there is evidence of equally 

 small irregular suborbitals {s.o.). The mandible is sometimes 



