LAMKID^. 
349 
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 
difiTerent parts of the mouth, the satisfactory determination of the 
extinct s{>ecies of the various genera of Lamnidae is almost impossible. 
The following arrangement is thus in a great measure provisional. 
Genus ORTHACODUS, nomen nov. 
Syn. L. Agassiz (non Sphenodon, Gray, IS.*!!, uec 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 Lamnid®. Each tooth consists of a 
slender, erect, more or less compressed crown, placed upon the 
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 Cladodus and certain species assigned to Hyhodxts. 
Orthacodns longidens (Agassiz). 
1843. Lamna {Sphenodus) hngidens, L. Agassiz, Poiss. Foss. vol. iii. 
p. 298, pL ixxvii. figs. 24-29. 
184C. Sgualtts phiUipgii, C. Rouillier, BulL Soc. Imp. Nat. Moscou, 
pt. ii. pi. B. fig. 0. (Name given, loc. cit. 1847, pt i. p. .372.) 
18.32. Oxyvhina longideng, F. A. Quenstedt, llandb. Petrefakt. p. 172, 
pl. xiii. fig. 11. 
1852. Oxyrhina macer, F. A. Quenstedt, op. cit, p. 172, pi. xiii. fig. 18. 
1852. O.ryrhina ornati, F. A. Quenstedt, op. cU. p. 173, pl. xiii. fig. 1.3. 
1858. Oxyrhina omaii, F. A. Quenstedt, Der Jura, p. 467, pl. btiii. 
%• 5. 
(?) 18M. Sphenodus, F. A. Quenstedt, op. cit. p. Ot‘2, pl. Ixxxi. fig. 30. 
1858. Oxyrhina macer, F. A. Quenstedt, op. cit. p. 783, pl. xevi. figs. 
45, 40. 
1800. Sphenodus macer, H. Trantschold, Bull. Soc. Imp. Nat. Moscou, 
pt. ii. p. 356, pL viii. figs. 23, 24. 
1861. Sphenodus macer, H. Trautschold, Zeitschr. deutsch. geol. Gesell. 
vol. xiii. p. 433. 
1861. Sphenodus longidens, II. T rautschold, tom. cit. p. 433. 
1875. Sphenodus macer, K. Fricke, Palseontocr. vol. xxii. p. 394, 
pl.xxi.fig.21. 
