]0 
l^^AUTILOTDEA. 
Orthoceras arcuoliratum, Hall. 
1847. Orthoceras arcuoliratum, Hall, Pal. of New York, vol. i. p. 198, 
pi. xlii. If. 7, a, h, c. 
? 1852. Orthoceras {Cycloceras) arcuoliratum^ H'Coy, Britisk Pal. Foss, 
fasc. ii. p. 319. 
? 1859. Orthoceras arcuoliratum, Salter, Quart. Journ. Geol. Soc. vol. xv. 
p. 375. 
1863. Orthoceras arcuoliratum, Billings, Geol. of Canada, Appendix, 
p. 949. 
? 1873. Orthoceras arcuoliratum, Salter, Cat. of Cambr. and Sil. Foss, 
p. 71. 
? 1882. Orthoceras arcuoliratum (?), Blake, British Foss. Ceph. pt. i. 
p. 84, pi. iii. f. 14. 
8p. Char. “ Slender, very gradually tapering to an acute point ; 
surface marked by strong and extremely arched or undulating 
annulations, and, obscurely, by fine longitudinal striae ; annulations 
about equalling the spaces between them ; outer chamber and aper- 
ture unknown ; section circular ; siphuncle central. 
“ The distinguishing features of this species are its slender form 
and extremely arched annulations, which, in half the circumference, 
ascend twice the width of the space between each annulation.” 
{Hall.) 
HemarTcs. Three small, chalcedonized fragments from the Durness 
Limestone are referred to this species. They exhibit the strongly 
arched annulations characteristic of Orihoc. arcuoliratum. 
Horizon. Durness Limestone ( = Calciferous (?) of North America). 
Localities. British. Durness, Sutherlandshire. — Foreign. Allumette 
Island, Biver Ottawa, Canada. 
Fairly well represented in the Collection. 
Orthoceras, sp. 
Two imperfect fragments, consisting of two or three septa, may be 
referred provisionally to the same form as that mentioned by Brogger 
Die silurischen Etagen 2 und 3,’ Kristiania, 1882, p. 24), as 
“ Orthoceras nah bei 0. regulare, Schloth.” 
The siphuncle is small and slightly eccentric. The septa are 6 or 7 
lines distant in a diameter of 2| inches. The test is not preserved. 
Horizon. Oskarskal Group, 4 (=Bala?). 
Locality. Birko, Norway. 
Orthoceras junceum, Hall. 
1847. Orthoceras junceum, Hall, Pal. of New York, vol. i. p. 204, 
pi. xlvii. ff. 3, a-f. 
