312 EOCENE MOLLUSCA. 
the sinus ; the posterior margins are rather deeply channeled, and are thickened round 
the suture, where they are girt by two or three fine, raised lines, decussated by 
numerous, rather coarse plications. The concentric lines in the hollow part of the 
margins and over the shoulders are numerous, slender, sharp, and regular; over the 
middle and front parts of the whorls rise several prominent, rather thick, ridge-like 
lines, varying in number and thickness in different individuals ; and over the inter- 
mediate spaces two or three fine, thread-like lines are generally found, although in 
some specimens, in which the ridges approach more closely, these intermediate lines 
are wanting; all the lines are decussated by the sharp, perspicuous lines of growth 
giving a finely reticulated aspect to the surface of the shell. The aperture is ofa long, 
narrow-oval shape, and terminates in front in a wide, very short, and indistinct canal, 
deeply notched at the extremity; the outer lip is almost semicircular, thin, sharp on 
the edge, and smooth within; the inner lip is rather thick, projecting, and curved 
outwards at the anterior extremity; the columella is very slightly twisted and bears, 
about the middle, a single, obscure, fold-like callus ; the front part presents a strongly 
marked crest, due to the anterior notch. The sinus is placed on the shoulder of the 
whorl, and is deep and moderately wide, with nearly parallel margins. 
The present species is very variable in the ornamentation; the most common and 
most strongly marked variety (Var. (3) is the one figured in ‘ Mineral Conchology’ (tab. 
exlvi, fig. 8), in which the tubercles on the shoulders are prominent and without the 
transverse furrow found in the typical form ; and the concentric lines over the middle 
and front parts of the whorls are obscurely denticulated. 
The shells figured and described by Sowerby as P. co/on are, as that author sug- 
gested, the young of Solander’s species. Jn the young state the proportions of the spire 
and of the body whorl are nearly equal, and the character of the ornamentation on the 
shoulders of the whorls is more strongly marked ; and in the figure given by Brander, 
P. turbida is represented as having a wider shell and a more pointed and slenderer 
spire than, in fact, characterise the species. Without an examination of the shell in 
all stages of growth, therefore, a doubt of the identity might reasonably be entertained. 
The shell described by Lamarck as P. turdida, in forgetfulness, probably, of that 
name having been already used by Solander, is a Sub-Apennine shell, which had already 
been named Murex cataphractus by Brocchi; and this circumstance may have led to 
the English shell having been at one time referred to Brocchi’s species, from which, 
however, it is quite distinct. 
Deshayes also has referred to P. colon some shells from the Soissonnais, which, 
although presenting a close resemblance to the present species, are specifically distinct ; 
the prominent and strongly crenulated band round the suture of those shells, resembling 
that found in P. alligata, is quite different in character to the margination in P. 
turbida ; and although the crenulation on the shoulders of the whorls resembles that 
which is found in the present species, it may have arisen from some variation of 
