<^xxoj£ A^<*-y6/t<^/z*y /^ pp uc - y 
349 
LAMNID2E. 
#r*, ^ ^ 
- Family LAMNID.F. 
Dorsal fins without spines, the first situated opposite to the space 
between the pectoral and pelvic fins. No nictitating membrane. 
Gill-openings generally wide \ spiracles minute or absent. Teeth 
solid when completely formed, pointed, and in most genera relatively 
large. 
Owing to the considerable variation in the form of the teeth in 
different parts of the mouth, the satisfactory determination of the 
extinct species of the various genera of Lamnidse is almost impossible. 
The following arrangement is thus in a great measurejprovisional. 
> / - 
Genus ORTHACODUS, nomen nov. 
Syn. Sphenodus,~L. Agassiz (non Sphenodon , Gray, 1831, nec Sphenodon, 
Lund, 1839), Poiss. Foss. vol. iii. 1843, p. 288. 
An extinct genus, known only by detached teeth, and provision¬ 
ally assigned to the family of Lamnidse. Each tooth consists of a 
slender, erect, more or less compressed crown, placed upon tho 
centre of the anterior margin of a horizontally expanded root. The 
latter is not forked or divided, and resembles the root of the tooth 
in Claclodus and certain species assigned to Hybodus. 
\ 
Orthacodus longidens (Agassiz). 
1843. Lamna ( Splienodus ) longidens , L. Agassiz, Poiss. Foss. vol. iii. 
p. 298, pi. xxxvii. figs. 24-29. 
1846. Squalus phillipsii, C. Rouillier, Bull. Soc. Imp. Nat. Moscou, 
pt. ii. pi. B. fig. 6. (Name given, loc. cit. 1847, pt. i. p. 372.) 
1852. Oxyrhina longidens , F. A. Quenstedt, Handb. Petrefakt. p. 172, 
pi. xiii. fig. 11. 
1852. Oxyrliina macer , F. A. Quenstedt, op. cit. p. 172, pi. xiii. fig. 18. 
1852. Oxyrhina ornati, F. A. Quenstedt, op. cit. p. 173, pi. xiii. fig. 13. 
1858. Oxyrhina ornati , F. A. Quenstedt, .Der Jura, p. 467, pi. lxiii. 
fig. 5. 
(P) 1858. Sphenodus, F. A. Quensted*, op. cit. p. 662, pi. lxxxi. fig. 36. 
1858. Oxyrhina macer , F. A. Quenstedt, op. cit. p. 783, pi. xevi. figs. 
45, 46. 
* rp 
. 
1 ' 
1860. Sphenodus macer, H. Trautschold, Bull. Soc. Imp. Nat. Moscou, 
pt. ii. p. 356, pi. viii. figs. 23, 24. 
1861. Sphenodus macer , H. Trautschold, Zeitschr. deutsch. geol. Gesell. 
vol. xiii. p. 433. 
1861. Sphenodus longidens, H. Trautschold, tom. cit. p. 433. 
1875. Sphenodus macer , K. Fricke, Palaeontogr. vol. xxii. p. 394, 
