The Shell-Collector’s Handbook. 7 
rachidian series are denominated by the sign 1 when 
present, and 0 when absent ; the admedian teeth by 
the signs 1, 2,3... . according to the number pre- 
sent ; while the lateral teeth are noted by the sign 0, 
repeated as often as there are lateral teeth on either 
side; when the number of admedian or of lateral 
teeth is very large, the sign x is used in place of 
1,2,3 ....or 0 repeated. For example, when, as 
in Afolis, there are no lateral teeth, we write the 
formula 0.1.0; that of Amphisphyra, is 1.1.1; 
that of Aplysia, 13. 1.13; and that of Onicidium, 
54. 1. 54.” (Jeffrey Bell. Comp. Anat. p. 136). In 
some of the Helices, the teeth may reach the enor- 
mous number of 39,596. The manner of the working 
of the radula may easily be observed by watching a 
Limnea stagnalis cleaning the conferve from the 
_ glass side of an aquarium. 
The buccal mass passes back by a thin-walled 
esophagus into a spindle-shaped cavity, the crop, 
which lies in that part of the visceral hump 
situated in the body whorl, and at the sides of which 
two large white salivary glands* open by means of 
their ducts, one on each side. Following the aliment- 
ary canal still on, we next come toa slightly dilated 
portion of it, which is known as the stomach, and which 
lies near the commencement of the second turn of 
spiral, close to the surface of the visceral hump. 
Then leaving this, we arrive at the commencement of 
* Recent researches show that this salivary gland contains 
free sulphuric and free hydrochloric acid, and that there can be 
but little doubt it has an amylolytic function in converting 
starch into sugar. 
