6 BULLETIN 73, UNITED STATES NATIONAL MUSEUM. 



The lachiymal is irregularly ohlong, 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 exteniled posteriorly beyond 

 the exoccipitals, which is a character indicative of age. 



The supraoccipital has a distinct median ridge, witli a longitudinal depression 

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



MANDIBLE. 



The mandible is slender, with a very elongate symphysis, which measures 2.37 

 mm. The inferior outline of tlie 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 coronoiil j)rocess. At about the beginning of the posterior fourth 

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

 coronoid ]u-ocoss. 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 tlistally in a rounded aperture 

 6 mm. in diameter, l)elow whicli 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 tiie alveolar groove becomes nar- 

 rower gradually and (iisa]ipears in a length of about 140 mm. 



The mental foramen is situated in line with the antciior base of the tooth, and 

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

 shallow groove runs along the inferior margin of the symphysis. 



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

 anteriorly. 



TEETH. 



The mandi])ular 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 

 antcro-posterior breadth, 28; transverse thickness, 10; lieight of apex above 

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

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

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

 of the base of the dentine crown, 12. 



This tooth, as alreadj' 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 margiD is broken at this point. 



