SUPPLEMENT^. 
Genus ORTHOCERAS. 
Orthoceras sulcatulum, M‘Coy. 
1844. Orthoceras sulcatuhun^ M‘Coy, Synops. Garb. Foss, of Ireland, 
p. 8, pi. i. f. 4. 
1876. Orthoceras suhcentrale, Armstrong, Young, and Robertson, Cat. 
of Western Scottish Fossils, p. 59. 
Sjy. Char. Shell elongate, tapering at the rate of about 1 in 4. 
Transverse section nearly circular. Septa distant from each other 
one fifth the diameter of the shell. Test ornamented with irregular 
waved riblets, which are much coarser in the adult shell than in 
the young ; they are often displaced, showing that the shell sus- 
tained fractures (probably at the aperture) and was afterwards 
repaired by the animal. 
Remarks. Having had the opportunity afforded me, through the 
courtesy of Mr. John Young, of seeing some fine examples of the 
present species in the Museum of the University of Glasgow, I must 
confess myself still unconvinced that 0. sulcatulum is identical with 
0. suhcentrale of de Koninck, The figure of the last-named species 
represents a shell with regular transverse riblets, without the 
slightest undulation in them, and much coarser, more equal and 
direct than those of 0. sulcatulum., in which the riblets are irregular 
and most distinctly waved. 
On again examining Sowerby’s type-specimen of 0. teres (see ante., 
p. 121) and comparing it with an example of 0. sulcatulum procured 
by myself at the Arden Quarry, I now feel pretty certain that 
0. teres is the young of 0. sulcatulum. 
Horizon. Upper Limestone Group 
Locality. Arden Quarry, Nitshill, near Glasgow. 
Represented in the Collection by a single example. 
‘ Consisting of a few species inadvertently left out of their proper places, and 
one ( Orthoceras sulcatulum) added to the Collection during the progress of the 
present volume. Also note on Ascoceras from Sweden ; and on a specimen of 
Orthoceras annulatum, from Dudley. 
* See footnote, p. 121. 
