ORIHOCERATID-E. 
117 
uncommon in which the cicatrix is preserved upon the initial point 
as figured by Hyatt and reproduced by Barrande (1878, loe. cit.). 
It consists of a little elongate cleft or depression, having the direc- 
tion of the long axis of the shell. This interesting phenomenon is 
observable in one of the specimens in the Xatioual Collection, from 
BoUand, Yorkshire. A specimen from Tournai, Belgium, shows zig- 
zag bands of colour, such as H. de Koninck mentions as occurring 
in a specimen from that locality recorded by him in 1844 (Descrip, 
des Anim. Fossiles &c.). 
Remarhs. This species is subject to great variation in outline 
owing to compression, because of the extreme tenuity of the test. 
The species nearest to it is Ortliocera^ Cyrtoceras”) digitus, de 
Kon., in which, however, the section is circular, and the siphuncle 
nearer the margin than in 0. unguis. 
Horizon. Carboniferous Limestone ; Calcaire Carbonifere (As- 
sise vi.). 
Localities. British. Bolland, Yorkshire. — Foreign. Vise, Tour- 
nai, Belgium. 
Represented in the Collection by numerous specimens from 
Yorkshire and Belgium. 
Orthoceras tenue, de Koninck, sp. 
1351. Cyrtoceras tenue, de Koninck, Descrip, des Anim. Fo.ssiles de 
la Belgique (Supplement), p. 50, pi. li.v. f. 5. 
1880. Cyrtoceras tenue, de Koninck, Faune du Calc. Carbonifere de la 
Belgique, p. 22, pi. xxxvi. f. 13. 
Sp. Char. This small species is remarkable for its slight and 
irregular curvature and very slender form. It is generally curved 
only at the apex, often being nearly straight for more than two 
thirds of its length. The initial point is obtuse and very slightly 
curved. Xo trace of the cicatrix has been found. The transverse 
section is circular. The septa are numerous and very close to each 
other ; regularly convex, and not deep. The body-chamber does 
not appear to have been very large. The siphuncle is very slender 
and filiform ; it is eccentric, and situated between the centre and 
the margin. The surface of the test is perfectly smooth. 
Remarks. C. subulare, de Kon., which is the nearest to this 
species, is distinguished by its less slender and shorter proportions.^ 
Horizon. Calschiste de Touimai = Carboniferous Limestone. 
Locality. Tournai, Belgium. 
Fairly well represented in the Collection. 
