152 CRETACEOUS GASTROPODA 
The sutural margin of the last whorl is thickened, the upper portion slightly 
excavated, and naturally also the space between the keels on the periphery. The 
aperture is nearly circular, internally smooth; the posterior canal is distinct, and also 
the fold-like tooth near the same; the outer lip has a slightly undulating peristome 
the inner lip is very thick, with the anterior fold distinctly marked; the columella 
widely excavated and the canal produced, its margins approaching anteriorly very 
closely so as to leave only a narrow slit open. The anterior portion of the canal is not 
preserved in any of our specimens, but, to conclude from the remaining indications, it 
seems to have been somewhat contorted and laterally curved, asin Tud. porphyrostoma. 
Casts of this species are almost identical with Pyrula planissima, Binkhorst (Mono- 
graph. Gast. et. Céph. de Limbg., p. 8, Pl. V2, Fig. 3), for which reason we have given 
a representation of a similar cast in Fig. 8); but who can vouch for the identity of 
these two fossils! According to Binkhorst’s Fig. 8c, the European species seems to 
have the inner lip less thickened, especially near the posterior canal, and the whorls 
more evenly rounded in the circuit. Until better specimens are found of the Meest- 
richt fossil, nothing can be done save to keep both forms under separate names. 
Localities.—N. E. of Karapaudy and near Arrialoor, in the Trichinopoly 
district ; not rare. 
Formation.—Arrialoor group. 
XXXVITI.—RAPA, Klein, 1758. 
Char. Rapa testa pyriformi, spira brevi ; ultimo anfractu ventricoso ; antice canali 
prolongato; columella excavata ; apertura subrotundata; labio levigato, antice 
upplanato, margine externo excavationem columelle sepius partim tegente. 
“ Rapa,” say H. and A. Adams in their Genera, I, p. 187, “ differs from Rapana 
not only in the produced canal of the aperture and thin simple whorls, but in the free, 
reflexed inner lip and moderate umbilicus.” The distinction indicated in the living 
KR. papyracea, Lam., to which Chenu added the R. twbulosa, seems equally to exist 
in the fossil species, and it is therefore desirable that the same ought to be generically 
noticed, specially as the fossil forms seem to be by far the more numerous. A marked 
characteristic of Rapa seems to be throughout common, namely, that the anterior 
canal is proportionally much longer in young than in fully grown specimens of the 
same species. This is a well known fact in Rapa papyracea, and we have here 
occasion to exhibit it on the cretaceous BR. cancellata, Sow. (compare the figures on 
Plates XII and XIII). It is probable that this distinction is valuable as regards 
Tudicla, in which such an alteration of form has not been observed. 
The relation of the shell of Rapa to that of Murex is about the same as that of 
Tudicla ; and from Rapana it differs in an equal degree, as Cuma from Monoceros. 
The number of fossil and especially cretaceous forms belonging to Rapa seems 
to be very great, as has been noticed previously, but the usual want of the canal in 
the fossil state makes the determination very often uncertain, 
