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PALEONTOLOGY OF NEW-YORK, 
GASTEROPODA OF THE LOWER HELDERBERG GROUP. 
The species of this class of fossils are much more numerous in the Lower 
Helderberg group, than in any of the preceding or succeeding palaeozoic 
periods below the Coal measures. They include, moreover, the greatest 
extremes, as well as a great variety of forms. We have the slender spiral 
shells with numerous closely arranged volutions, as in Murchisonia and 
Loxonema, and the broad ovoid forms with one or two volutions at the 
apex; the slender forms with the volutions free, and the conical or 
broadly depressed-conical forms which are straight or nearly straight, 
having no evidence of convolutions whatever, or with a slight arcuation 
at the apex. 
Notwithstanding all this variety of form and degree of development in 
the spire, there is but a single nodose species known to me in this period; 
and in this one, the nodes are rather like transverse interrupted ridges # . 
The surfaces of many species are spirally or longitudinally ridged, and 
often transversely or concentrically lamellose or lamellose-striate, while 
a few forms are strongly cancellate. 
Two species of Euomphalus are known in the strata of this age, and a 
single species of Bellerophon or Bucania. The few species of Loxonema 
and Murchisonia are unfortunately in the form of casts, and their study 
is thus rendered unsatisfactory. 
A large number of the forms are such as are at the present time re¬ 
ferred to the Genus Capulus of Montfort ( Pileopsis of Lamarck), with 
which Acroculia of Phillips and Platyceras of Conrad are made synony¬ 
mous. For certain other forms among these shells, Mr. Conrad proposed 
* The earliest nodiferous or properly spiniferous form of gasteropod occurs in the Oriskany sandstone, 
the casts of which are strongly nodose, and the shell ornamented with strong spines. The spine-bearing 
gasteropods are common in the Upper Helderberg group, and are known in the Hamilton group and in the 
Carboniferous limestones. 
