﻿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 of a 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 (Far. (3) is the one figured in ' Mineral Conchology ' (tab. 

 cxlvi, 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. colon are, as that author sug- 

 gested, the young of Solander's species. In 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. turbida, 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 



