Hello Helmut,
 
I believe the name "dog" in reference to a shell is an old English
expression meaning commonplace or ordinary.  In the case of Strombus
canarium of course, the specific name literally means dog, hence the
common name "dog conch".  However, there are other species where the
common name "dog" is used, even though the scientific name doesn't
mean dog, such as Nucella lapillus (dogwinkle) and Glycymeris
glycymeris (dog cockle).  The scientific name vulgaris (vulgare) is
similar in meaning - ordinary, nothing special.
 
Paul M.