W. H. Hudleston—On the Yorkshire Oolites. 109 



occur at intervals immediately above the Cynocephala-zone (Yellow 

 Sands). ^ But when we come to what was once the more calcareous 

 portion of the Dogger, the shell-bed towards the top is so lull of 

 them as to have received the name of Nemicea-hed. In this bed, 

 only 18 inches thick, the first noteworthy accumulation of Nerinceas 

 occurs, nor are they ever plentiful again throughout the Yorkshire 

 Oolites until we reach the Corallian Rocks. 



How and whence did they come, these curious cylindrical shells 

 with their internal folds ? Such a question must occur as a matter 

 of course to every one interested in Jurassic palgeontology. The 

 genus is so well marked and characteristic, and, on the whole, so 

 different from anything else that a close attention to its genesis may 

 ultimately lead to conclusions of importance in the biological history 

 of the Mesozoic rocks. Does the evidence at present in our posses- 

 sion lead us to suppose that they appeared almost simultaneously 

 along the whole line, or earlier in one place than in another ? We 

 may fairly believe that these shells originated in the calcareous 

 shallows, which succeeded the more sandy deposits of the Cynocephala- 

 zone towards the base of the Inferior Oolite. As far as our English 

 beds are concerned, Nerincea first appeared on this horizon, which 

 may be regarded as situate in the lower portion of the MurcJiisonce- 

 zone ; we shall perceive this fact more clearly in studying the 

 relations and distribution of N. cingenda, Phil., the oldest so far as 

 we know of the race. 



Most of the specimens found in the Dogger belong to that species. 

 In the next, or Millepore zone, are a few specimens, some of which 

 may belong to other species. The condition of these fossils is for 

 the most part so indifferent, that they have usually been referred 

 without question to Nerincea cingenda. The same may be said of 

 specimens from the Scarborough Limestone of Cloughton (Hundale). 

 Beyond the fact that they are cylindrical Nerinceas, with prominent 

 spiral belts at the base of each whorl, nothing more can be said 

 about them. In the Cornbrash Nerincea is extremely rare individually, 

 but contains two well-marked species, whilst the Kelloway Rock, 

 Oxford Clay, and Lower Calcareous Grit are devoid of it. But as 

 soon as the deposits become markedly calcareous, as in the Lower 

 Coralline Oolite, then Nerincea once more puts in an appearance, and 

 swarms in the true Coralline Oolite and Coral Rag. 



Glancing at the history of the appearance of Nerincea in other 

 areas, we find Nerincea cingenda, Phil. (i.e. Bronn), to be the only 

 representative of the genus in the Northampton Sand, on the horizon 

 of the Dogger, where it is stated to be rare ; whilst both this and 

 several other species are quoted from the Lincolnshire Limestone.'^ 

 Again, in the Inferior Oolite of the Cotteswolds, N. cingenda is the 

 only species quoted by Wright from the Pea Grit, etc., of Cheltenham,^ 

 whilst several species made their appearance in the overlj'ing Oolite 

 Marl.* Further south the evidence of the occurrence of Nerincea as 



^ See Yorkshire Oolites, pt. i. Proc. Geol. Assoc, vol. iii. 



2 Judd, Geology of Rutland, p. 282. ^ q_ j_ q_ g. vol. xvi. pp. 11 and 13. 



* First noticed and described by Lycett in 18o7. See his " Cotteswold Hills." 



