OKTHOCERATIDJE. 
115 
iS44. OrtJioceras Gesneri, de Koninck, Descrip, des Anim. Fossiles de 
la Belgique, p. 520, pi. xlvii. f. 4. 
? 1854. Orthoceras costellatum, Roemer, Palfeontographica, Band iii. 
p. 92, tab. xiii. f. 24. 
1855. Orthoceras {Campyloceras) Gesneri, M‘Coy, British Pal. Foss, 
fasc. iii. p. 570. 
1860. Orthoceras Gesneri, Eichwald, Letliaea Rossica, vol. i. Seconde 
Sect, de Tancienne PMode, p. 1220. 
1862. Cyrtoceras tuberculatum, Griffith, Journ. Geol. Soc. of Dublin, 
vol. ix. p. 55. 
1876. Cyrtoceras Gesneri, Armstrong, Young, and Robertson, Cat. of 
Western Scottish Fossils, p. 58. 
Sp. Char. Shell straight, or slightly curved. Section oval in 
adult specimens, nearly circular in the young. Rate of increase 
about 1 in 8. Septa simple, moderately numerous, averaging two 
lines apart. Siphuncle near the margin in the young, but ai^fwoaching 
nearer the centre in the more aged. Surface ornamented with from 
22 to 36 strong, equal, regular, narrow, prominent ridges, separated 
by slightly concave spaces, averaging twice the width of the ridges ; 
the whole covered by very fine, transverse, raised lines, which in 
crossing the ridges form little arched squamae, giving a nodose 
appearance to the ridges. 
Remarhs. This species has given rise to much difference of opinion 
among authors, especially as to whether the small, slightly curved 
specimen figured by Xartin (f. 2) bo the same as the largo one (f. 1). 
M. de Koninck regards the former as a Cyrtoceras, on account of 
its curvature ; but, as I have already remarked elsewhere, that is a 
feature which is verj- commonly met with in the genus Orthoceras, 
especially in the section Anr/ulati, to which the present species be- 
longs, and therefore it cannot be considered of generic value. 
The difference in the position of the siphuncle represented in 
de Koninck and Phillips’s figures is probably due to the difference 
in age of the individuals described by them. Such a change in 
position is by no means uncommon in Cephalopods, both recent and 
fossil. 
With regard to the tuberculation existing upon the ridges in 
this species, Professor M‘Coy remarks that as his Cyrtoceras tuher- 
cidatum was founded upon this character, it must merge into Martin’s 
species, as has been already recognized by M. de Koninck in his 
supplement.” It should be remarked that the Belgian specimens 
have a slower rate of tapering than the English ones. 
Honzon. Carboniferous Limestone. 
Localities. British. Bolland, Yorkshire. — Foreign. Tournai, Bel- 
gium. 
