Vol. 5] 



Merria m. — A Primitive Ich th yosauria n . 



387 



tend the whole length of the skull fragment and reach down to 

 the lower border of the ramus. They are very thin behind the 

 middle of the orbits, but gradually thicken until their diameter 

 immediately anterior to the orbits is several times that opposite 

 the middle of the orbits. The angular seems to be represented 

 by a small splint bone situated between the surangular and the 

 splenial just behind the middle of the 'orbit. 



The frontal region is unfortunately only imperfectly pre- 

 served, considerable portions of all of the elements represented 

 having disappeared before the specimen was discovered. The 

 frontals extend back to a point a little behind the middle of the 

 orbits, where the specimen is broken off posteriorly. The an- 

 terior ends of the frontals extend forward almost to the posterior 

 ends of the superior narial openings. Along the superior side 

 of the skull a prominent median ridge is developed at the point 

 of union of the frontals. • 



The prefrontals are large and extend well in toward the 

 median line of the skull. The centers of radiation of the struc- 

 ture lines of the prefrontals are situated a little behind the 

 anterior borders of the orbits. The anterior ends of the pre- 

 frontals extend forward to the posterior ends of the narial 

 openings. 



The lachrymals are large and form the greater part of the 

 anterior borders of the orbits. The lower end of each lachrymal 

 extends back as a slender splint along the maxillary. The limits 

 of the upper posterior border are not distinctly shown, but seem 

 nearly to reach the superior margin of the orbit. The anterior 

 end of the lachrymal extends very near to the posterior end of 

 the superior narial opening. Almost exactly opposite the middle 

 height of the anterior border of the orbit the lateral portion of 

 the lachrymal is extended outward as a prominent, triangular 

 knob. 



The superior narial opening is evidently represented on one 

 side of the specimen by a very distinct depression occupying 

 almost exactly the same position in the facial region as the 

 narial opening of the ichthyosaurs. The nasal elements border 

 the narial openings above, and extend forward to the anterior 

 end of this specimen, where the terminations are exceedingly 



