51 
l. Yerus. 
The shell ventricose, covered with a horny periostraca, which is 
more or less covered in the different species with a polished shelly 
coat, deposited by the expanded mantle. The spire is short, and 
irregular ; the aperture expanded. 
The animal is large, compared to the size of the shell, when ex- 
panded. It is ovoviviparous; the young when born being of a 
large size, and covered with a shell with a large irregular callous apex. 
The foot is large, partly covering the shell, which is sunk into its 
substance. Operculum wanting. 
Confined to the coast of Africa and the shores of the Medi- 
terranean. 
The best character for the distinction of the species of this genus 
depends on the extent which the mantle covers the shell, shown in 
the shells themselves by the size of the polished coat. Unfortu- 
nately, the original surface, indicating the extension of the mantle 
over the surface of the shell, in this and other genera of this family, 
is often destroyed in cabinet specimens, even in the most recently- 
formed collection, which greatly deteriorates from their scientific 
value, and great care should be taken to observe that the specimens 
desired to be determined have not been injured in this respect. 
Mr. Adams, by some oversight, observes, when referring to this 
genus, “ These shells are uniform in colour, sombre, covered with 
an epidermis, and with a deciduous nucleus.’ (Genera, 159.) 
Several species are marbled; some have the epidermis covered with 
a glassy coat; and I am not aware that any shell has the nucleus 
deciduous, much less this genus, when they are enclosed by the 
older whorls. 
A. The only species found in the Mediterranean has a narrow 
deep channel near the suture ; the shell is one-coloured, and the left 
side of the mantle and inner lip of the shell is much expanded over 
the last whorl. 
1. Yerus Ouxa. 
Voluta Olla, Linn. 
Voluta papillaris, Gmelin. 
Cymbium Olla, Menke, Adams, 150. 
Cymba Olia, Brod., Sow. Spec. Conch. 7. f. 1 a, 4, ¢, d. 
Cymbium papillatum, Schum. 237. 
Hab. Mediterranean. 
B. The species found on the coast of Africa have a broad wide 
channel on the suture of the shell. They may be divided into three 
groups :— : 
* The left side of the mantle and the inner lip of the shell rather 
expanded ; the shell is mottled. 
2. Yetus Navicuta. 
Spire short. 
Voluta Navicula, Gmelin. 
