IN GENERAL. 683 
downwards, and turned the ligament forwards. BLAINVILLE, on 
the contrary, described it in the position which we have indicated}. 
In the univalves (cochlee, teste univalves, subbivalves) the fol- 
lowing parts may usually be distinguished. The extremity of the 
spire is called the point (apex), which, when the animal is alive and 
in motion, is turned upwards and backwards. Ordinarily the cavity 
of the shell terminates in a point at this part, but it is sometimes 
truncated horizontally (apex decollatus s. truncatus), which must not 
be mistaken for an accidental fracture which always leaves an open- 
ing. In some univalve shells (as in the genus Patella), the cavity 
between the point and the aperture is neither twisted to the right or 
left, nor forwards or backwards. In most, on the other hand, this 
cavity is turned. Usually all the turns run obliquely from above 
downwards (turbinated shells, cochlea turbinata et turrita); yet in 
some the wreaths or turns run from left to right in a transverse 
direction, whereby the last wreath includes the rest externally (testa 
convoluta s. involuta, the involute shell, as in the genera Conus and 
Oliva), whilst others again are turned in one and the same vertical 
plane, from behind forwards and from above downwards (cochlea 
revoluta, as in the genus Nautilus). 
The opening (apertura) of the shell is opposite to the point. 
That part of the cavity, which is visible within the mouth, is called 
the throat (faux). The mouth may be excised with a sinus ante- 
riorly (apertura emarginata). Whenever it terminates forwards in 
a channel (apertura canalifera), then the tube is called the tadl 
(cauda s. rostrum). At the mouth the external margin (labiwn 
exterius 8. labrum) is distinguished from the internal margin (labiwm 
internum s. margo columellaris). The spindle (columella) is that 
part which runs in the middle of the shell directly from the point to 
the aperture, and round which, as an axis, the wreaths are tumed. 
Such a calcareous axis is not present in all univalve shells; to see 
this part distinctly, a shell sawn longitudinally must be provided. 
At the internal margin of the aperture there is often on the ex- 
tremity of the spindle, especially in the shells of younger molluscs, a 
cavity which is called navel (umbilicus). Shells, in which this aper- 
ture is wanting, are named ¢mperforate (cochleee imperforate). 
1 That which with Linnaus is the right and the left shell still preserves this 
name, since he turned the bivalve not only upside down, but also the fore part 
backwards. 
