8 CRETACEOUS GASTROPODA 
appear indisposed to adopt a division of the old genus, Helix, into smaller groups 
under different names. And there can be no question that such sub-division is 
rendered quite necessary even in the present imperfect state of our knowledge 
of all the respective animals. 
With all the apparent similarity, the variation in the form of the shell and 
coincidently, to some extent, in that of the animal itself, is still so manifold, that it 
is not easy to characterize even the sub-family Helicine, in its restricted sense, as 
given in the more recent Conchological treatises. But what the characteristics 
of the genus Helix in Lamarck’s sense might be, is readily seen when we read in 
Woodward’s Manual, or Bronn’s ‘ Klassen und Ordnungen’ a. o., that it comprises 
shells of discoid, globular and conical form, umbilicated, perforated or imperforated ; 
with a transverse, oblique, lunar or round aperture; with its margins distinct, 
remote or united by callus!! ete. No one can fairly or seriously object, if Con- 
chologists attempt to classify these and other so widely different characters under 
different names. 
Of this sub-family, Helicine, we notice two genera Anchistoma and Macrocyclis. 
T.—Ancuistoma, Klein. 1758. 
Anch. testa orbiculari, spira plana seu subconvexa ; anfractibus numerosis, 
subtus omnibus vel duobus ultimis conspicuis, sew wmbilico clauso ; ultimo anfractu 
prope aperturam contracto, deflexo atque nonnunquam gibboso ; apertura subrotundata, 
expansa, intus sepissime callosa, ad margines dentibus seu plicis muita. 
The genus ANCHISTOMA comprises a number of chiefly small species of Heli- 
cine, which are distinguished by a large number of narrow whorls, the last of 
which is deflexed and usually provided inside with some kind of teeth or plaits. 
The inner lip is mostly callose, tooth-like and projecting into the space of the 
aperture, while the outer lip is expanded and reflected. There can be no doubt, 
that the species attributed to this genus, as they can be seen amply illustrated on 
plates 64—66 in Pfeiffer’s “ Schnirkel-schnecken” 1846, form a sufficiently natural 
group to be distinguished by a separate name. Among themselves they present, 
however, several characters which seem to make a still farther sub-division into 
small groups very desirable. We notice in general the helicoid and non-umbili- 
cated forms with somewhat elevated spire, and the more planorboid and umbili- 
cated forms. Among these again those which have all their previous volutions 
visible in the space of the umbilicus, and others in which the last or the two last 
whorls are so much enlarged below, as to cover this space nearly totally. Simi- 
larly to this the dentition of the aperture varies. The peristome is only somewhat 
thickened and expanded; or there are a number of plaits or folds present in the 
inside of the whorls, disappearing near the mouth partially or totally ; or there are 
differently shaped teeth at the peristome only and not extending into the inner 
spaces of the whorls. 
