The Collaborative International Dictionary of English v.0.48:

Rhachiglossa \Rhach`i*glos"sa\, n. pl. [NL. See Rhachis, and
   Glossa.] (Zool.)
   A division of marine gastropods having a retractile proboscis
   and three longitudinal rows of teeth on the radula. It
   includes many of the large ornamental shells, as the
   miters, murices, olives, purpuras, volutes, and
   whelks. See Illust. in the Appendix.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Murex \Mu"rex\, prop. n.; pl. Murices. [L., the purple fish.]
   (Zool.)
   A genus of marine gastropods, having rough, and frequently
   spinose, shells, which are often highly colored inside; the
   rock shells. They abound in tropical seas.
   [1913 Webster]