192 
NATJTILOIDEA. 
Surface of the test smooth, or marked only with minute striae of 
growth. 
Remarks. The changes in the nomenclature of this species are 
thus explained by Prof. M‘Coy : — I have been obliged to give a 
new specific name to this species, as Phillips’s 0. laterale, proposed 
as a substitute (in consequence of Sowerby’s specific name having 
been previously used by Schlotheim), differs from the true species of 
Sowerby in having much more distant septa and more nearly central 
siphon. To the present species may x)robably, however, be referred 
the 0. imbricatum from Marwood, figured in Phillips’s Palaeozoic 
Possils . . .” 
A. undulatum is said by M‘Coy to be “ rare in the Carboniferous 
Limestone of Closeburn, Dumfriesshire.” 
It appears from Sowerby’s observations upon this species that 
he was very doubtful about its being identical with Martin’s, for 
he says his [Martin’s] species is more rapidly acuminated or conical, 
in his “ the dissepiments are approximate, concave, oblique, almost 
entire . , . Sowerby adds : — “ This species is said to vary 
considerably in size ; we hope this figure will give occasion to inquiry 
whether they are the same species or not . . .” 
M. de Koninck {loc. cit. p. 74) makes the present species synony- 
mous with A. Breynii.^ Mart., sp. ; but they appear to me to be very 
distinctly separable, the latter having the septa horizontal and wider 
apart than they are in the former. The marked obliquity of the 
septa in the present species would at once distinguish it from A. 
Breynii. The fossil which de Koninck has identified (under the 
name of Orthoceras migrans^, not of Barrande) with the A. Breynii ?, 
Sow., sp. (non Martin), does not agree with that species at all. The 
septa are much wider apart in de Koninck’s form than they are in 
Sowerby’s, and, moreover, judging by the figure, they are quite 
horizontal. 
Horizon. Eed Sandstone Group of the Calciferous Sandstone 
series^ (Closeburn specimen) ; Carboniferous Limestone. 
Localities. British. Scaleber, near Settle (the type of A. undu- 
latum., Sow., sp.), BoUand, Yorkshire; Closeburn, Dumfriesshire; 
Orchard Quarry, near Glasgow. — Foreign. Yise, Belgium. 
Well represented in the Collection, which, amongst other ex- 
amples, includes Sowerby’s types of A. undulatum and A. Breynii ?, 
and a specimen from Closeburn, bequeathed to the Museum by Sir 
W. C. Trevelyan, Bart. 
^ See ante, p. 20. 
See footnote ante, p. 121. 
