50 CRETACEOUS GASTROPODA 
4. Cypreovula is distinguished by its transversal striation, which replaces on 
the outer lip the dentition, and forms thus a passage to the next genus. The Oyp. 
Oapensis is at present often met with in the collections, and there are several tertiary 
species known, which exhibit the characters of this genus very well. 
5. Triviais characterised by its spiral (usually called transversal) striation, being 
secreted from the mantle and replacing the dentition on the margins of the aperture, 
where these striz become often somewhat changed in their form and tooth-like. 
Morphologically speaking, the strize in Zrivia, and the marginal teeth of the 
aperture in other genera of cypra#iva are identical. The two sub-genera Pus- 
tularia and Epona, as quoted by H. and A. Adams (loe. cit. p. 269) include rather 
characteristic forms, and will, we think, form good generic distinctions ; namely, 
6. Species, which are commonly somewhat depressed, and tuberculated or 
corrugated on the back, are assigned to Pustularia. 
7. The shells of Apona are globose, mostly smooth, and with both anterior 
and posterior extremities much prolonged and contracted. 
8. The genus Erato will be noticed in more detail hereafter. 
9. Pseudocassis was established in 1863* by Messrs. Pictet and Campiche for 
a single cretaceous species, Psewdocassis helveticus. The specimens examined were 
only casts without any trace of shell or enamel-coating. The authors state, that 
there is no trace of teeth, or of any rugosity on either of the margins of the aper- 
ture. In my ‘ Reyision of the Gastropoda of the Gosau-formation,’+ I have, doubt- 
fully, referred to this genus the Ovula striata of Zekeli, and at the same time, I 
have drawn attention to some indistinct crenulation on the outerlip of this species. 
So far as I can remember, there is nothing more to be noticed regarding the doubtful 
Pseudocassis striata, than I have already mentioned (loc. cit.) and for a decision on 
this point better materials must be obtained. It is, however, not impossible, that my 
suspicion (loc. cit. p. 63) of its being a Cyprea may be proved correct. The speci- 
men figured by Zekeli has evidently the enamel surface wanting, and consequently 
the spire exposed: it is certainly not an Ovwla, and, in any case, it belongs to the 
cypr@in&. Having recently had much occasion to observe closely the state in 
which fossil Cypree occur, I confess I am rather anxious to see, what results will 
be derived from an examination of the typical species of Psewdocassis, when it is 
met with complete with the shell preserved. A case in point happened to me 
lately. I had the description of the Cyprea Kayei, as a Pseudocassis, based upon 
the specimens figured on Pl. IV, Figs. 8—10, ready for more than a month: when, 
fortunately enough I found afterwards among our materials two other specimens, of 
one of which the representation is given, Fig. 7, and this, having had the shell partly 
preserved and being prepared with the greatest possible care, decided the point exactly 
in the contrary way. On a specimen of Ps. helveticus, very kindly presented to the 
Museum of the Geological Survey of India by Prof. Pictet, I cannot but persuade 
myself, that some impressions along the outer peristome have been originated by 
* Paléontologie Suisse. 3me Ser. 2. pt. p. 361. 
7 Sitzungsb. Akad. Wien. Bd. LII., 1865, 
