﻿DISCOHELIX. 



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Cirrus nodosus is very abundant at Coker — the most abundant species accord- 

 ing to J. Buckraan. It also occurs in the irony nodule-bed (Murchisonae-zone) at 

 Burton Bradstock, whence splendid specimens are sometimes obtained. It is 

 also met with at Stoford, at Bradford Abbas, and at Dundry. I have not seen 

 any representative of this species from the Cotteswolds. 



Note on Discohelix and Straparollus. 



I have already indicated that Discohelix may be regarded as a sub-genus of 

 Straparollus, which, if we accept the views of d'Orbigny, is the same as Enom- 

 phalus, Sowerby- It is evident that Straparollus, as interpreted by d'Orbigny, 

 included Discohelix. On the other hand, Mons. Cossmann (' fit. Bath.') is inclined 

 to refer most of the Bathonian species of Straparollus to Solarium. 



There certainly does seem to be a sort of gradation between the flat and 

 biconcave form of the most typical Discohelix through the several species of 

 Straparollus into Solarium. But in the latter genus the whorls slope towards 

 the apex, whereas in Discohelix and Straparollus they are more or less flat, like a 

 strap-coil. Hence Solarium is more easily separated from Straparollus than the 

 latter is from Discohelix. 



In the following diagnosis of Discohelix and Straparollus the peculiarities of 

 the Inferior Oolite forms have been more especially studied, and it is by no means 

 pretended that such a diagnosis of Straparollus would be found wholly applicable 

 to the Palaeozoic species thus named. 



I should be rather inclined to classify under one genus all the forms which, 

 in the following pages, have been assigned to Discohelix and Straparollus. With 

 this proviso the two following diagnoses are submitted. 



Genus — Discohelix, Dunher, 1847. 



Shell discoidal, depressed, more or less biconcave; whorls arranged in flattened 

 coils round, a centre, squared at the periphery and furnished with two marginal heels, 

 usually tuberculated ; aperture quadrangular. 



Genus — Straparollus, Montfort, 1810. 



Shell discoidal, more or less depressed; the under side largely e.rea rated ', fhe upper 

 side flat, or with the spire slightly raised in, steps ; whorl* roiled like straps, somewhat 



