178 CRETACEOUS GASTROPODA 
With these characteristics we would restrict the name Nerinea to the much 
elongated and turreted shells, which have the last volution built in a perfectly sym- 
metrical way to all the other whorls, so as not to exceed them considerably in size 
and form. It is angulated at the basal periphery, and terminates abruptly in a short, 
anterior canal. Each whor! has below the suture a narrow band, formed of solid 
shell-mass, on which, however, in cases of good preservation, fine insinuated lines 
of growth are traceable. This band, of which we shall always speak as the “ su- 
tural band,” recalls, according to D’Orbigny, the somewhat similar form in 
Pleurotomaria. I have never had an opportunity of observing any Nerinea with 
perfectly preserved aperture, and cannot therefore say whether there is a posterior 
emargination present or not ; if it is, as no doubt would appear very probable, it can be 
only small, for I did not observe it in nearly perfect specimens of Ner. Bucht and 
nobilis. I have also not been able to get very distinct sections of the shell, but it seems 
to me that the shell-mass which constitutes this sutural band is rather more in con- 
nection with the thickening of the inner than with that of the outer lip. Below the 
suture the strize of growth are always curved in an S-form, depending upon a simi- 
lar curve of the margin of the outer lip. 
There are usually three or four folds present on the inner and two on the outer 
lip. Of the former, two are, strictly speaking, placed on the columella, the anterior 
stronger than the posterior, and two in a similar position on the inner lip, which 
forms the top of the angular aperture. I have consequently called them in my for- 
mer notes on Nerinea the top-folds (vide Sitzungsb. Akad. Wien, 1865, LIT, Revi- 
sion ete. p. 25); they might perhaps be better called posterior folds. But it is 
scarcely necessary to make always these subordinate verbal distinctions, unless a 
special importance is attached to them. If figures of specimens be not given, 
lengthened descriptions and explanations cannot be avoided. Of the two columellar 
plaits the posterior is, although nearly always smaller, generally present, but it dis- 
appears often sooner towards the aperture, than the other plaits. Still in process 
of growth all the plaits in the interior of the whorls become usually thicker and 
often fill up the space perfectly. In consequence of this the uppermost whorls be- 
come often easily corroded, having been placed out of connection with the organism 
of the animal. 
The columella is usually solid or only fissured on the last whorl; seldom it is 
hollowed out in its entire length as in the jurassic Nerinea grandis and dilatata, 
D’Orb., but it is always distinctly twisted. 
10a. By far the larger number of the MNerinee with a hollow columella 
are eretaceous ; they are mostly smooth shells, with angular whorls contracted in 
the middle, and three plaits in the aperture, one columellar, one posterior plait, and 
one on the outer lip. It is possible that in these forms another small group of 
Nerinee may be distinguished, but I am quite unable to come to any certain con- 
clusion, as I have nothing but mere figures to compare, and these refer often to 
casts of shells only. The doubtful Pyramidella sagittata, Sharpe, (Quar. Jour. Geol: 
Soc. VI, 1850, p: 198, Pl. XX, Fig. 8) belongs evidently to this group. 
