NERINiEA. 217 



153. NEiiiNiEA (Ptygmatis) bacillus, D'Orbigny, 1850. Plate XV, figs. 5 a, 'jh, Q a 



— c, 7 a, and Plate XVI, fig. 12. 



1850. NERiNiEA BACILLUS, UOrh. Prod., i, p. 298. 



1852. — — — Ter. Jurass., ii, |). 8i, pi. cclii, figs. 3 — 0. 



1884. — {Ptygmatis) bacillus, lyOrh. Cossmaun, Et. Batli., p. 19(3, 



pi. i, figs. 25 and 26, and 

 pi. xi, fig. 18. 



BlbliograjJhl/, Sfc. — The specimens from the Batboniau of Marquise figured by 

 D'Orbigny are represented as Laving 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 Paleontologie Fran^aise. In our Inferior Oolite there are varieties of a 

 species so closely resembling the Nerinsea bacillus of the Terrain Jiirassique that 

 I can hardly venture to give it a diflPerent name. 

 General Description .• 



Spiral angle . . . 3° — 4°. 



Height of whorl to width . . from 1 : 1 to 1 : 1"1 



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, hb, 6 b, and 6 c), 

 but the posterior fold on the columellar side, i. e. the fold on the posterior wall, 

 is simple and very sUght, 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 diff'ers 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 



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