400 CRETACEOUS GASTROPODA 
2. (Auriculina), Gray, 1847, non idem, Grateloup, 1838 (H. and A. Adams, 
Gen., I, p. 233). ‘Shell ovate, thin, ventricose, whorls simple or concentrically 
striated, columella edentulate, without a plait.’ H. and A. Adams considered 
Auriculina as a sub-genus of Odostomia, but A. Adams (Ann. mag. nat. hist., 
1860, V, p. 407), when describing Awriculina Grayi (dredged in 63 fathoms of 
water), says that it may more probably belong to the Acrzonzp#, and it seems 
to me that it is the representative of the fossil genus Acte@onina. I have no 
recent shells belonging to Awriculina to compare, but I strongly suspect that 
they will be found generically identical with Act@onina, in which case it will be 
unnecessary to propose for the recent shells a new name. 
3. Luconacteon, Meek, 1863 (Americ. Jour. Se. and Arts, XXXV, p. 91) is 
distinguished by its ¢hin, obconic shell, gradually tapering anteriorly, the spire is 
either immersed or elevated, the aperture very long, equally narrow all through, 
anteriorly rounded, columella slightly thickened, smooth. The typical forms 
Hue. Caumontii and concavus of Deslongchamps and others very much resemble 
in form a Conus, from which they differ by their very thin shell and the anterior 
roundness of the aperture. The surface is usually smooth or spirally striated, 
and the spire is plane or somewhat immersed. The thinness of the shell and its 
regular obconic form, inasmuch as the last whorl is not suddenly contracted 
towards the anterior termination and the aperture not sensibly widened in front, 
must be considered the principal generic distinctions from Act@onina. Meek 
(loe. cit., p. 92) suggests for the Conus Cadomensis of Deslongchamps the sub-generic 
name Conacteon, but I do not think that the distinction, referring to the elevation 
of the spire, can be considered sufficient, for the same reasons which I have stated 
when speaking of Acteonina. 
The species of Huconacteon, so far as known at present, are all jurassic. 
4. Cylindrites, Morr. and Lyc., 1854 (Moll. Great Ool., p. 97). Shell sub- 
cylindrical or ‘ovate, smooth, spire sunken or moderately elevated, aperture narrow, 
very high, anteriorly rounded, sub-effuse, columella twisted anteriorly into a distinctly 
conspicuous fold. 
The Cylindrites differ from <Acteonine by the twisted columella; they are 
like these generally smooth. Meek (loc. cit., p. 91), again proposes for a few species, 
like Cyl. brevis, M. and L., and others which have a very short or immersed spire, 
a sub-genus, Goniocylindrites, but the distinction of a separate name cannot 
be accepted. 
I only know as yet triassic and jurassic species belonging to this genus. Meek 
refers to it Conus cylindraceus, Geinitz, which is probably a Cylichna. Gabb 
described a Oylindrites brevis (non idem. M. and L.) which is either an imperfect 
shell belonging to some genus of the rzvercvriv™, or has to be considered as the 
type of a new genus. I shall subsequently mention a somewhat similar form from 
our cretaceous rocks. 
Some of the species of Cylindrites very closely approach in form to Ceritella 
(or Zubifer, see antea p. 189), which is, however, stated not only to possess a twisted 
