6 BULLETI>- rS. UNITED STATES NATIONAL MUSEUM. 



The lachrymal is irregularly oblong, with an external free margin 35 mm. long 

 and 12 mm. tliick. The distance from the anteorbital notch to the anterior end of 

 the orbit is 60 mm. (PI. 7, fig. 1.) 



The lateral free margins of the basioccipital are extended posteriorly beyond 

 the exoccipitals, which is a character indicative of age. 



The svipraoccipital has a distinct median ridge, with a longitudinal depression 

 on each side, bounded externally by a proniinent convexity. (PI. 10, fig. 1.) 



MANDIBLE. 



The mandible is slender, with a very elongate symphysis, which measures 237 

 mm. The inferior outline of the ramus is strongly concave at the middle and 

 slightly convex posteriorly, while the symphysial portion is bent upward. The 

 superior outline is concave both behind and before the tooth, and also immediately 

 anterior to the coronoid process. At about the beginning of the posterior fourth 

 the outline is convex, and the mandible at this point is nearly as deep as at the 

 coronoid process. The superior surface of the symphysis slopes down on each side 

 to the median line, but each half of the surface is itself nearly plane. (PI. 11, figs. 

 1, 2, and 5.) 



The alveolar groove anterior to the tooth is very distinct throughout and is 

 without septa and open at the bottom. It ends distally in a rounded aperture 

 6 mm. in diameter, below which are several small foramina. These lead to a very 

 large canal which occupies all the symphysial portion of the mandible, the walls 

 being comparatively thin. Behind the tooth the alveolar groove becomes nar- 

 rower gradually and disappears in a length of about 140 mm. 



Tlie mental foramen is situated in line with the anterior base of the tooth, and 

 is confluent with a groove which extends forward for about 80 mm. A rather 

 shallow groove runs along the inferior margin of the symphysis. 



The coronoid process is erect and rounded, and is joined by a horizontal ridge 

 anteriorly. 



TEETH. 



The mandibular tooth, which is shown in PI. 2, fig. 3, is preserved on the right 

 side only. Its dimensions are as follows: Length anteriorly in a straight line, 75 

 mm.; length from the apex to the posterior end of the root, straight, 60; greatest 

 antero-posterior breadth, 28; transverse thickness, 10; height of apex above 

 internal superior margin of jaw when tooth is in situ," 22; antero-posterior length 

 of base of exposed portion, 30; distance from anterior end to posterior end of root, 

 37; greatest height of the exposed dentine crown, above the cement, 14; length 

 of the base of the dentine crown, 12. 



This tooth, as already stated, is only two-thirds as broad and three-fourths 

 as long as that of Sowerby's Brodie House specimen (the type of the species), 

 which was an adult male, and leads to the belief that the Nantucket specimen was 

 a female. This is in a manner confirmed by the Rugsund specimen, which was an 

 adult male and had teeth as large as Sowerby's specimen. It has to be remarked, 



« The external margin is broken at this point. 



