NERIN^A. 193 



" 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 everyone 



interested in Jurassic palaeontology Does the evidence at present in 



our possession lead us to suppose that they appeared almost simultaneously along 

 the whole line, or earlier in one place than another ? We may fairly believe that 

 these shells originated in the calcareous shallows which succeeded the more sandy 

 deposits of the Gynocephala-'&tdige towards the base of the Inferior Oolite." 



Since the above was written the attention of Mr. Witchell and others has 

 been drawn to this very question, and I myself have had many opportunities for 

 extending the investigations, which originally commenced in Yorkshire, into the 

 Midland and South-western Counties. The following is a partial summary of the 

 results. 



There is no authentic evidence of the existence of Nerinsea in the British Lias, 

 although the late Charles Moore enumerates four species.^ In Yorkshire Nerinsea 

 has not yet been detected below the Nerinsea-hed which occurs in the upper part 

 of the Dogger at Blue Dyke. Here a well-known and well-developed form 

 {N. cingenda, Phil.) suddenly appears in abundance, and a large variety of the 

 same species appears with equal suddenness in the Northampton Sand. In the 

 Cotteswolds several species of Nerinsea appear in the Pea-grit, mostly cylindrical 

 forms belonging to the sub-genus Ptygmatis. These are undoubtedly in the 

 Murchiso7ise-zone. But in the shell-bed below the Lower Limestone at Crickley 

 Hill, in what is perhaps the top of the Opalinus -zone, occurs a Nerinsea {Ptygmatis) 

 to which I have given the specific name of xenos, possessing an internal structure 

 considerably diflferent from that of N. cingenda. This appears to be the oldest form 

 of Nerinsea hitherto discovered in the Cotteswolds, and it serves to bear out the 

 general conclusion that the genus, as far as this country is concerned, makes its 

 first appearance on the confines of the zones oi Am. MiircJiisonse and Am. opalinus. 

 In Dorsetshire, on the other hand, where a strong cephalopod facies characterizes 

 all the zones, Nerinsea is as unknown in the Inferior Oolite as in the Lias.'^ 



We owe much of our knowledge of the Nerineeas of the Cotteswolds to the 

 ability and enthusiasm of the late Mr. Witchell, of Stroud, who literally died at 

 the edge of his favourite quarry on Swift's Hill, whither he was in the habit of 

 repairing for the purpose of extracting fossils. In his admirable paper " on the 

 genus Nerinsea and its stratigraphical distribution in the Cotteswolds " Mr. 

 Witchell enumerates twenty species from the Inferior Oolite of that region, these 

 being classified under five groups according to their internal structure. 



It is well known that many attempts have been made to subdivide this 



^ Some of these are founded on very imperfect fragments. " Nerina3a " liassica is stated by 

 Mr. Walford to be a Gerithiuni, as proved by the section. 



^ For further information relative to the distribution of Nerinsea see Introduction, especially 

 p. Gl. 



25 



