NERlNvEA. 211 



Heiglit of whorl to width (mean about) . 1 : 1*25. 



Approximate length . . . 100 — 140 mm. 



Shell subcylindrical, turrited. Whorls numerous, and variable in relative 

 proportions, but on the whole rather high. At first the sutural belt or carina is 

 very prominent, and the whorl very concave (13 h). Presently the whorls are 

 divided almost equally by a median belt, the anterior portion being excavated 

 whilst the posterior portion is flat. Fine spiral lines with faint granulations are 

 usually present, but appear to fail in the anterior whorls, where a considerable 

 modification takes place, though, on the whole, the somewhat long whorl, the 

 median varix, and the constricted anterior area are usually characteristic. 



Available specimens rarely have a good aperture, and the actual body-whorl is 

 seldom seen. Fig. 13 a shows a good aperture, with one wide fold rather below 

 the centre of the outer wall, and two finer folds on the columella. It is 

 probable, however, that this is not the real body-whorl, but merely the lowest 

 whorl of an imperfect specimen.^ The very small posterior fold on the outer 

 wall may not have been developed in this particular case. The section is shown in 

 figs. 13 rf and 13 e, both from the Dogger of Blue Wyke. It may be described as 

 triplicate to quadruplicate. The posterior fold on the outer wall is small, and not 

 always present in every whorl of the same specimen. Fig. 14 represents a cast 

 of a fragment of a large specimen from the ironstone of Irchester, where the 

 posterior fold of the outer wall has been developed on one whorl and not on 

 another. 



Relations and Distribution. — In Yorkshire Nerinsea cingenda occurs abundantly 

 in the upper part of the shell-bed towards the top of the Dogger at Blue Wyke, 

 but has never yet been found in any part of the Dogger below that bed. It may 

 also occur in the Millepore Bed, though I have not been able to identify it 

 for certain.^ From its proneness to dimorphism, and the variability of its internal 

 section, it affords an excellent example of the instability of the genus, of which in 

 Yorkshire it is the first representative. The two species, or sub-species, next 

 described are its more immediate relatives. 



As regards distribution in other parts of England, N. cingenda may usually be 

 looked for on the Dogger-horizon in the counties of Lincoln, Rutland, and 

 Northampton, although I only know of it myself in the last county. Many of 

 the large casts in the Duston ironstone belong to this species. As we proceed, 

 south-westwards there seems to be an indication of it in the Inferior Oolite of 

 Otley Hill. I have never seen genuine specimens from the Cotteswolds, although 



^ See antea, p. 195. 



2 Although I possess several iuteresting fragmeuts from the Millepore-bed, one of which is a 

 Ptygmatis, tliey are too imperfectly preserved for description. In the Scarborougli Limestone, as is 

 usual where a Cephalopod facies predominates, Nerincca is hardly to be found. 



