ACTIN0CEKATID2E. 
181 
1831. OrtJioGeratites imhricatus, Hisinger {non Wahlenberg), Anteclm. 
i Pbysik ocb G eognosie, Haft. v. p. 112, tab. iy. f. 4. 
1837. Orthoceratites imhricatus, Hisinger, Letbaea Syecica, p. 29, tab. ix. 
f. 9. 
1842. Orthoceratites imhricatus, Eicbyald, Die Urwelt Russlands, 
Heft ii. p. 24. 
1845. Orthoceratites imhricatus, Murcb., de Vern., and de Keyserl. G^ol. 
de la Eussie d’Eiirope, yol. ii. pt. 3, Paleont. p. 393. 
1852. Orthoceras imbricatum, Giebel, Faima der Vorwelt, Band iii. 
Abtb, i. p. 247. 
1857. Orthoceras imbricatum, BoU, Arcbiy flir Mecklenburg, xi. Jabrg. 
p. 21, Taf. yi. ff. 18, a-c. 
1858. Orthoceras {Ormoceras) imbricatum, Scbmidt, Arcbiy fiir die 
Isaturkimde Liy-, Ebst- und Kmdands, Baud ii. Lief. i. p. 194. 
1860. Actinoceras imbricatum, Eicbwald, Letbaea Eossica, Seconde 
Section de I’ancienne Periode, yol. i. p. 1253. 
1866. Orthoceras 2>seudo-imhricatum, Barrande, Syst. Sil. de laBobeme, 
vol. ii. Texte iii. 1874, p. 705, pi. ccxxyiii. f. 1, pi. ccxxxiii. ff. 4-8, 
pi. ccccxl. ff. 1, 2. 
[Ao^ 1821. Orthoceratites imhricatus, Wablenberg, Noya Acta Eeg. 
Soc. Scient. Upsaliensis, yol. yiii. p. 89. — 1870. Orthoceras imhri- 
catum ?, Barrande, loc. cit. p. 701, pi. ccccxl. ff. 3, 4. — 1882. Or- 
thoceras imbricatum, Blake, British Foss. Cepb. pt. i. p. 153, pi. 
xiy. ff. 1, 1 «, 3, 3 a, 4, 4«, 5, 6.] 
Bp. Char. Shell straight, rather rapidly tapering at the rate of 
about 1 in 9. Section apparently circular. Septa very approximate, 
the sutures forming a conspicuous sinus on the sipbuncular aspect 
of the shell and sweeping upwards in a bold curve till they meet on 
the opposite side. In consequence of this they are oblique to the 
long axis of the shell, the angle of obliquity being about 22°. The 
diameter of the siphuncle (measuring the inflated part of it) is about 
that of the shell. Traces of the endosiphon and of the tubuli 
which connect it with the septal chambers are seen in polished 
sections. The outer test is unknown, bat a fragment of what would 
appear to be the inner layer is perfectly smooth. 
EemarJcs. The type described by Wablenberg is stated to have an 
extremely slender, filiform, central siphuncle, and therefore it could 
not have belonged even to the same genus as Hisinger’s A. imbri- 
catum, much less to that species. 
Barrande, to escape from this dilemma, appealed to Angelin, who 
supplied him with specimens which he had collected in the island of 
Gothland, and which he said he believed to be the species described 
by Wablenberg under the name of Orthoceras imbricatum. There 
then remained Hisinger’s imbricatum to be dealt with, and upon that 
Barrande bestowed the name of pseuclo-imbricatum. 
