28 THE PLAGIOSTOMIA. 



SCAPANORHYNCHUS. 



Rhinognathus Davis, 1887, Trans. Roy. Dub. soc, ser. 2, 3, p. 480. 

 Scapanorlujnchus Woodward, 1889, Cat. foss. fishes Brit, mus., 1, p. 351. 

 Milsukurina Jordan, 1898, Proc Cal. acad. sci., scr. 3, 1, p. 200. 



Body long, slender; snout elongate, with a much produced rostrum. 

 Mouth large, protrusive, inferior, with labial lolds. Teeth subulate, with two 

 rooted bases. Eyes without nictitating folds. Spiracles present. Gill open- 

 ings five, wide. First dorsal above the space between pectorals and ventrals. 

 Tail long, without lateral folds or caudal pits. Caudal fin long. 



This genus dates from the Cretaceous; at present it contains a single 

 known living and four or five fossil species. It is most closely allied to Carcharias 

 as founded by Rafinesque, with which most of the fossil species have at some 

 time been identified, under the name Odontaspis. 



SCAPANORHYNCHUS OWSTONI. 



Plate 40 (brain); Plate 51, fig. 1-6 (general anatomy); Plate 56, fig. 2 (heart). 



Milsukurina owstoni Jordan, 1898, Proc. Cal. acad. sci., ser. 3, 1, p. 200, pi. 11-12; Jord. & Fowler, 



1903, Proc. U. S. nat. mus., 26, p. 621, pi. 26, 27; Bean, 1905, Proc. U. S. nat. mus., 28, p. 815, fig. 

 Scapanorhynchus owstoni Woodward, 1899, Ann. mag. nat. hist., ser. 7, 3, p. 487; Howes, 1902, Proc. 



Brit, assoc. adv. sci., p. 626; Dean, 1903, Science, 23, p. 630; Vaillant, 1904, Comp. rend. Acad. 



sci. Paris, 138, p. 1517; Regan, 1906, Proc. Zool. soc. Lond., p. 744; Dofl., 1906, Ostas., p. 256, 



fig.; HussAKOF, 1909, Bull. Amer. mus., 26, p. 257, fig. 

 Scapanorhynchus jordani Hussakof, 1909, loc. cit., p. 257, pi. 44. 



Body elongate, slender, compressed; head depressed, length to the fifth 

 gill opening nearly one third of the total length; snout very long, pointed, 

 broader than deep, longer than the skull behind it; rostral cartilage simple 

 anteriorly, deeper than wide, posteriorly in three branches, two upper and one 

 lower, as in Carcharias. Nostrils small, oblique, near mouth and eye, anterior 

 valve with a rudimentary lobe above the internal partition of the sac. Eyes 

 small, not as wide as the nostril, pupils vertically elliptical, diameter of orbit 

 two thirds of its distance from the nostril or half the distance from the spiracle. 

 Mouth large, protrusible, somewhat extensible; a labial fold on the lower jaw 

 only, hardly one fourth of its length. Teeth with slender awl-shaped cusps and 

 broader two-rooted bases, in ||z|| rows; those in nine or ten rows at the angles 

 of the mouth very small, irregular and without the long cusp ; lateral teeth with 

 a denticle on the base at each side cf the cusp, anterior teeth larger, without the 

 denticle; anterior tooth of lower series much smaller than the next one to it. 

 A larger space between the third and the fourth teeth of the upper jaw near the 



