DISCOHELIX. 315 
Cirrus nodosus is very abundant at Coker—the most abundant species accord- 
ing to J. Buckman. It also occurs in the irony nodule-bed (Murchisonx-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 DiscoHEetix 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 Huom- 
phalus, Sowerby. It is evident that Straparollus, as interpreted by d’Orbigny, 
included Discohelix. On the other hand, Mons. Cossmann (‘ Et. 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 Solariwm. 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 Solariwin is more easily separated from Straparollus than the 
latter is from Discoheliv. 
In the following diagnosis of Discoheliv 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 Paleozoic 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 Discoheliv and Straparollus. With 
this proviso the two following diagnoses are submitted. 
Genus—DisconEix, Dunker, 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 keels, 
usually tuberculated ; aperture quadrangular. 
Genus—StRaParoLLus, Montfort, 1810. 
Shell discoidal, more or less depressed ; the under side largely excavated, the wpper 
side flat, or with the spire slightly raised in steps ; whorls coiled like straps, somewhat 
