OKTHOCERATID^. 
Horizon. Or/^ocdm^-Limestone ( = Ai-enig). 
Locality. Prussia ? 
[Also a specimen from I^orway, presented by Dr. Kjerulf, from 
the Oskarskal Group, 4 (=Bala?).] 
Fairly well represented in the Collection. 
Orthoceras politum, M‘Coy. 
1851. Orthoceras politum, M^Coy, Ann. & Mag. Nat. Hist. ser. 2, 
Tol. vii. p. 45. 
1851. Oiihoceras politum, Salter, in Murchison, Quart. Journ. Geol. 
Soc. Yol. yii. p. 137, pi. x. ff. 5, 6. 
1852, Orthoceras politum^ M‘Coy, British Pal. Foss. fasc. ii. p. 316, 
pi. i. L. f. 30. 
1865. Orthoceras politum, Haswell, Silurian Formations of the Pent- 
land HiUs, pi. i. f. 1. 
1870. Orthoceras lancea, Barrande, Syst. Sil. de la Boheme, toI. ii. 
Texte iii. 1874 (ianvier), p. 640, pi. ccclxxix. f. 10, pi. ccccx. 
ff. 1-14, ? pi. ccccxi. f . 8. 
1870. Orthoceras lancea ?, Barrande, Distrib. des Ceph. dans les Con- 
trees Siluriennes, p. 50 (Extrait du Syst. Sil. de la Boheme, yoI. ii. 
4me ser.). 
1870. Orthoceras lentum, Barrande, Syst. Sil. de la Boheme, vol. ii. 
Texte iii. 1874, p. 641, pi. ccccxxi. ff. 3-8, pi. ccccxlii. ff. 24, 25. 
1870. Orthoceras potens, Barrande, Syst. Sil. de la Boheme, vol. ii. 
Texte iii. 1874, p. 540, pi. ccxix. ff. 5, 6, pi. ccclxxxv., pi. ccclxxxvi. 
ff. 1-6, pi. ccclxxxviii. ff. 4-6, pi. cccciv. ff. 1-3. 
1873. OHhoceras politum, Salter, Cat. Camhr. & Silurian Foss. p. 70. 
1876. Orthoceras laricea?, Tromelin & Lebesconte, Assoc. Fran^. pour 
Tavancement des Sciences, 4me Sess. (Nantes), p. 621, and Tabl. D, 
no. 29. 
1878. Orthoceras, sp., Bayle, Explication de la Carte G6ol. de la France, 
tom. iv. Atlas, preni. part. pi. xxxiv. ff. 3, 4. 
1882. Orthoceras politum, Blake, British Foss. Ceph. pt. i. p. 141, pi. ix. 
ff. 1, 2, 8. 
\_Not Orthoceras politum, Klipstein, 1843, Beitr. z. Kenntn. der bst- 
lichen Alpen, p. 144, pi. ix. f. 6.] 
Sp. Char. Section circular. Bate of increase slow, not exceeding 
1 in 11. Septa direct, but sometimes slightly oblique ; distant 
from I to 5 the diameter, with a convexity of ^ to | the diameter. 
Siphuncle from T to ^ of the whole diameter, central in the young 
shell, but becoming eccentric with growth. Surface with fine trans- 
verse striae of growth. The type (in the Woodwardian Museum, 
Cambridge) is the longest example known. The species occurs also 
in the Silurian. 
Remarks. 0. politum differs from 0. vacjans in the regularity of 
its septa, the eccentricity of its siphuncle, and its less rapid increase. 
