96 
NAUTILOIDEA. 
Localities. Castletou, Derbyshire ; Caldbeck, Cumberland. 
Eepreseuted in the Collection by Sowerby’s types (“ Sowerby 
Collection”) figured in the ‘ Mineral Conchology and other examples. 
Discites bisulcatus, de Koninck, sp.h 
1844. Nautilus {Discites) sulcatus, M^Coy, Synop. Carboniferous Foss. 
Ireland, p. 19, pi. iv. f. 14. {Not of J . de C. Sowerby.) 
1855. Nautilus {Discites) sulcatus, M^Coy, in Sedgwick and M‘Coy’s 
British Pal. Foss. fasc. iii. p. 561. {Not of J. de C. Sowerby.) 
1878. Nautilus hisulcatus, de Koninck, Faune du Calcaire Carbonifere 
de la Belgiq^ue (Annales du Mus. Boy. d’Hist. Xat. de Belgique, 
tom. ii,), p. 128, pi. xxyii. fi*. 5, 6, 7, 9. 
Sp. Char. Shell discoid, lenticular, compressed, composed of three 
whorls, all exposed in a somewhat shallow umbilicus, which has a 
large central perforation. The initial extremity is pointed, and no 
cicatrix has been seen upon it. The section is oval at the com- 
mencement of the first whorl, but it soon becomes polygonal, and 
preserves this form until within a short distance from the aperture. 
The latter is subtriangular, truncated above, and a little more than 
one-third higher than wide. The surface is ornamented on the 
sides with three small longitudinal keels, which are equidistant 
and parallel ; the inside one forming the edge of the umbilicus is 
continued up to the aperture, whilst the other two become obsolete 
before the latter is reached. Besides the three keels just mentioned 
there is a fourth, situated in the upper third of the sides ; it is some- 
times double, and is only visible upon the last whorl, which covers 
it in the preceding whorls. On each side of this double keel is a 
rather shallow groove, the inner one of which only is seen throughout 
the whole extent of the whorls. 
The surface is covered with fine and regular lines of growth form- 
ing a sigmoid curve upon the sides of the shell and a deep sinus upon 
the periphery. 
The septa arc numeroiLs, there being thirty in the last whorl. 
The body-chamber occupies about half of the last whorl. 
The sipliuncle is situated between the centre and the peripheral 
border. 
Eemarlcs. De Koninck pointed out the distinctness of this species 
from the D. sulcatus of J. de C. Sowerby, and the evidence of the 
specimens in the British Museum Collection fully justifies his views 
upon the subject. It appears that M‘Coy had, -in the earlier copies 
of the plates illustrative of his ‘ Synopsis,’ called his species hisul- 
' Not M‘Coy, as de Koninck has it. 
