294: CRETACEOUS GASTROPODA 
In addition to the species previously (p. 40) noticed, I have to mention Tylost. 
lineatum, Bichwald (Leth. Rossica, XI, Livr., 1867, p. 8238, pl. 28, fig. 10) which in 
form resembles our Tylost. bulimoides ; the former species is stated to occur in the 
Neocomien of Antonowo on the mouth of the Oka river. The same author besides 
quotes from other localities of Russia TZylost. Rochatianun, T. Laharpi and 
T. depresswm, all previously described by Pictet and Campiche in the third series of 
the ‘ Materieaux pour la Paléontologie Suisse.’ 
The name Pterodonta has to be retained for species, of which the Pier. elongata, 
d’Orb., is the type, having a distinctly dilated outer lip, provided with an internal 
tooth and a more or less produced, or recurved, anterior canal. The species agree 
in form with some Strombi, like St. Lamarckii, but they usually appear to have 
a smooth shell. Pterodonta ovata would also be a species of this genus. How far 
the other species noted by D’Orbigny in his ‘ Prodrome’ are true Pterodonte, I have, 
as already stated, not been able to ascertain on account of the very defective state 
of the original specimens. 
What I have previously (pp. 39, 40, and 41) called ¢ypical species of Pterodonta 
are mostly true Tylostome, while on the contrary those few species, like P¢. gaultina 
and carinella of Pictet, and my Pt. terebralis, may possibly belong to Pterodonta. 
Pictet himself is not certain of the correctness of the generic determination of his 
two species; two others described by Seeley (vide p. 39) are also doubtfully distinct 
from Aporrhais, and the same may be said regarding my generic determination 
of Pt. terebralis. I should not be surprised, if the last named species proves to 
belong to the PrramipELi1p# or to the CrRrrHirpZ. 
Thus after all the numerous suggestions and alterations, which I have formerly 
proposed in the genus Pterodonta, it now appears that most of the species have 
again to be restored to Tylostoma, which most probably belongs to the family 
Naricip#. Ido not know a single genus of recent shells, which can be closely 
compared with the cretaceous Zylostome, though internal varices are found in some 
species of PrrammpELLipm, CeriTuiip#, ALATA, and in a few others. 
b. Sub-family,—NATICIN £4. 
1. Amaura, Méller, 1842, (H. and A. Adams’ Gen. I, p. 213,) has been restricted 
only to the turreted species, like 4. candida, MOll., from Greenland. With regard 
to its form this species may be considered as intermediate between the Nazicrp# and 
the cueunirziins (family Horrmips). 
2. Amauropsis, Morch, 1857, (H. and A. Adams’ Gen. II, p. 621), has been 
proposed for the two northern species, 4. canaliculata and A. cornea, the shells of 
which merely differ from Amaura by their more ovate and ventricose form. The 
spiral striation which is occasionally present is only superficial, and easily worn off. 
There is a large number of fossil species known, which as regards the form of their 
shells are not distinguishable from Amawropsis. These are thinner than those of 
Ampullina or Euspira, by which character alone they often can be distinguished from 
these allied genera. The two living representatives are inhabitants of the northern 
