NERIN MA. 217 
153. Nurinma (Piygmatis) Bacittus, D’Orbigny, 1850. Plate XV, figs. 5a, 5b, 6a 
—c, 7a, and Plate XVI, fig. 12. 
1850. Neninza Bacrttus, D’Orb. Prod., i, p- 298. 
1852. — — — Ter. Jurass., ii, p. 84, pl. eclii, figs. 3—6. 
1884. _ (Ptygmatis) Bactuius, D’Orb. Cossmann, Et. Bath., p. 196, 
pl. i, figs. 25 and 26, and 
pl. xi, fig. 18. 
Bibliography, §c.—The specimens from the Bathonian of Marquise figured by 
D’Orbigny are represented as having a whorl whose height and width are about 
equal. It is on the supposition that these figures are correct that the 
following comparisons are founded, as no measurements are given in the text 
of the Paléontologie Francaise. In our Inferior Oolite there are varieties of a 
species so closely resembling the Nerinwxa bacillus of the Terrain Jurassique that 
I can hardly venture to give it a different name. 
General Description : 
Spiral angle - : - d—4°, 
Height of whorl to width . from dls tod’ 
Length estimated up to . . 150 mm. 
Shell cylindrical and greatly elongated. Whorls numerous, about as high as 
wide, excavated, the chief constriction being rather below the centre and slightly 
increasing with age. Sutural belt prominent. In the young and the median stage 
the whorls are ornamented with about six spiral lines, which are somewhat 
unequally distributed, but, as is often the case, these have a tendency to 
disappear with age. 
The section shows seven folds more or less complex (see figs. 5 b, 6b, and 6c), 
but the posterior fold on the columellar side, i.e. the fold on the posterior wall, 
is simple and very slight, and scarcely to be seen in some of the volutions. 
The two anterior folds on the outer wall extend about halfway up, and are 
flat-headed with two projections. The posterior fold on this side is at some 
distance from these, and is also flat-headed with two projections. The anterior fold 
on the columella is large, deep, and bifid, in some cases with three angles; the 
second fold is narrow and slightly bifid ; the third is deep and very strongly bifid. 
Relations and Distribution —The interior structure differs but slightly from the 
description given by D’Orbigny of N. bacillus, and is very similar to that of 
N. Oppelensis presently to be described. Such differences as do exist may be 
partly the result of the conditions of preservation. Our Inferior Oolite varieties 
of Ptygmatis bacillus may be distinguished from Ptyg. Oppelensis by the greater 
28 
