484, MAZATLAN UNIVALVES 
Genus RAPANA, Scham. 
Essai, no. 57,1817. Shell Pyruloid: operculum Purpuroid. 
Supcenvus RHIZOCHEILUS, Séeens. 
Steenstrup, Afh. Ac. Copenh. May, 1850.—H. & A. Ad. Gen. 
vol. i. p. 185; (diagn. auct.) 
Rapana, pars, Phil. Handb. Conch. p. 487. 
Murex, pars, et Purpura, pars, auct. 
611. RuizocHEILus Nux, ve. 
Murex nux, ve. Conch. Ze. pl. 35, sp. 181 : (diagn. nune auct.)* 
Murex (Ocinebra) nux, H. & A. Ad. Gen. i. 75: [non Purpura 
(Polytropa) nux, doe. cit. 1. 128. ] 
PR. t. valde solidd, irregulari, albi; anfr. nucleosis lavibus, 
primo decollato ; spird seu depressd, seu elevaté ; costis radian- 
tibus v.-viil. tumidis, rotundatis, plus minusve prominentibus ; 
liris confertis spiralibus squamosis, interstitiis prefundis, plus 
aninusve angustis ; squamulis confertissimis, rotundatis : aper- 
turd ovoided, labro acuto, a sguamulis crenulato, intus denticu- 
lato; labio haud tenui, haud producto ; canali angustd, profunde 
excavatd, recurvata ; costa canaliferd solidd, intortd, rimam 
umbilicalem monstrante: operculo subpyriformi, nigro-fusco, 
margine tenut, diaphano ; nucleo in marginis externt medio sito. 
That this curious and very variable shell is not a Murex, is 
shewn by its Purpuroid operculum and want of varices. It is 
intermediate in character between Vitularia salebrosa and 
Cuma costata, more nearly approaching the latter. Although 
only bearing a general resemblance to the typical Rhizccheilus, 
yet as the species brought together by Messrs. Adams (under 
the subgeneric name Coralliophila) form a natural assemblage 
* The species in this group are so similar to each other, but the shells in each 
so variable, that their discrimination is a matter of extreme difficulty: especially 
as the types in Mus. Cuming have been so corroded by the acid process that the 
minute seulpture (which is one of the best criteria) is no longer visible. The 
type of Murex nux, Reeve, may therefore stand for whatever is wished : the 
Mazatlan shell is called after it on Mr. Cuming’s authority. The Panama shell 
brought by Mr. Bridges (at first named R. distans, Mr. Cuming regarding them 
as distinct) appears to be one among the many varieties of ‘‘R. niveus, A. Ad.” : 
nor does the acid allow of a distinction being evident between this and R. nux. 
The R. Californicus may be distinct, having a very large body whirl, with the 
ribs almost obsolete; but this again has lost its markings under the acid. [The 
Leucozonia Californica, Gulf of Cal. Lieut. Shipley, appears more nearly allied 
to Lathirus than to Leucozonia cingvlata.] 
