284. CRETACEOUS GASTROPODA 
5. Vanesia, A. Adams, 1861 (Ann. Mag. Nat. Hist., VITI, p. 242 and p. 307) 
has been proposed for two species,—V. trifasciata and V. sulcatina,— resembling 
in all their external characters JZelania, but being true marine shells; both the 
species are slightly ornamented with decussated transverse and spiral ribbings. 
These five genera, so far as at present known, may be considered as the 
representatives of a very large number of varied fossil shells. They are generally 
placed in the Prrammperzip#, but when we compare the animals of Aclis, Hbala 
and Hyala with those of the genera belonging to that family, we find that they 
want one of the principal characters, namely, the thickened and folded tentacles of — 
the Prramipetiip#z; the eyes are also placed nearer to the outer margins than 
to the middle ; the rostrum, the operculigerous lobes and other organs are found to 
be much more similar to those of the Rissozpz, than to those of the PrrammpELLIDaZ. 
Comparing the shells, we find them deprived of all columellar folds, chiefly 
_ differing from Zurbonilla or Eulimella by the less truncated and anteriorly more 
produced basis of the last volution, having in consequence a more elongated and 
ovately shaped aperture; the mammillate apex, which is found to be characteristic 
of many PrramipELiip2, is usually wanting in the species of the present family. 
The fossil species resemble in exterior form Melanie, but they are believed to 
be marine shells. Though generally very numerous in different deposits, they are 
on account of their insufficient preservation, still in many respects so doubtfully and 
imperfectly known, that we cannot pretend to give anything like a complete account 
of the genera, which have been proposed for them. As I have already mentioned 
they belong to the oldest known fossils, having probably their maximum in the 
triassic period. Some of the better known generic names are the following :— 
6. Pasithea, Lea, 1833, (Contrib., p. 99). The species are considered by Pictet 
to be generically identical with those of Chemnitzia. There are in reality, however, 
very different forms described by Lea under the name of Pasithea; some of them 
belong unquestionably to Hulima, others to Niso; one or two could be referred to 
Aclis, and there are only two species, P. guttula and Claibornensis, (1. cit., p. 104, 
pl. 4, figs. 86-87), which are distinguished by a very short spire and ventricose last 
volution. They resemble Macrocheilus, but it is possible that Lea’s original name 
can he reserved for these inflated forms, for they are rather more slender and cylin- 
drical than typical species of Macrocheilus generally are. Conrad (Check list eoe. 
foss., Smithson. Miscel. Coll. n. 200, p. 14) refers both the last named species to 
Hulima, which is hardly correct. 
7. Chemnitzia, D’Orb., 1889. This name, although first proposed for a series 
of shells belonging to Hlusa, Syrnola and Turbonilla of the Pyrraurprrrrps#, must 
be now retained in the sense, as stated in the Paléontologie francaise terr. Jur., 1850, 
Vol. II, p. 31. The principal characteristic distinction of the numerous species 
here figured seems to consist in the broad posterior insinuation of the outer lip, 
corresponding with the curve of the strize of growth. The smooth species cannot 
be generically separated from the ribbed ones, if those ribs have the same direction 
as the strie. The sharpened margins of the aperture distinguish the smooth forms 
