20 SUPPLEMENT TO THE CRAG MOLLUSCA. 
by the late Col. Alexander, but, unfortunately, it has no special locality attached. It is 
undoubtedly a Crag shell, and from its appearance it looks hike one of the Fluvio-marine 
specimens of Bramerton. ‘The sinistral form of 7. antiquus, occasionally found at the 
present day in the British seas, is simply striated, and not carinated, corresponding in 
that respect with the shell so abundant at Walton-on-the-Naze. 
In the ‘Crag Mollusca,’ vol. i, p. 45, I have expressed an opinion that this left-handed 
striated whelk was, in British seas, probably the original form, in opposition to the 
general statement of conchologists that it is merely a variety, in consequence of the dif- 
ference displayed from the common right-handed shell of the present day. 
The great majority of shelled univalved Mollusca haye the volutions turned in a dextral 
direction, that is, from left to right, but whether the original inflexion was given to the right 
or to the left we do not know, or why they should have taken the one in preference to the 
other. Among the Cephalopoda, the oldest known form is the straight one, as in 
Orthoceras. The bend from this seems to have been first in a vertical direction, such as 
Phragmoceras or Toxoceras. he deviation from that vertical direction was, I conjec- 
ture, due to the partial atrophy of the organs on one side, from a slightly altered position 
of the heart, until the highly oblique growth of the Zwrrilite was reached. 
Fusus sinistrorsus, Lam., is now an inhabitant of the Mediterranean Sea, and it is also 
a fossil in the newer Tertiaries of Sicily, and this may be a descendant of the older form 
of the Walton Crag sea. I can perceive no difference sufficient to constitute the 
Mediterranean shell a different species from the Crag fossil. It is, therefore, somewhat 
remarkable that m Zrophon antiquus this sinistral form should be the only one found in 
the Crag of Belgium, appearing there in the middle and upper beds, both dextral and 
sinistral forms being unknown in the lower, as they are also in the Cor. Crag of this 
country, thus apparently showing that the dextral form of this shell was of more modern 
origin than the sinistral, and that it had not appeared during the earlier part of the Red 
Crag. ‘The left-handed “ Almond Whelk”’ is the only form of this variable species which 
is found in the Red Crag of Walton-on-the-Naze (the whole fauna of which locality is, 
in my opinion, clearly older than that of any other part of the Red Crag) ; for while I 
have seen thousands of the sinistral shell from this locality, [ have never met with one of 
the dextral form there, or seen a specimen of it in the possession of any collector from this 
place. In the rest of the Red Crag the dextral and sinistral forms of the striated shell 
seem present in about equal proportions, and the same thing occurs in the Fluvio-marine 
Crag, in the Chillesford bed passim, and in the Lower Glacial sands of Belaugh, Rackheath, 
and Weybourne. In the Middle Glacial sands, however, the only trace of the sinistral form 
that has occurred is the pullus of some sinistral Zrophon, which is probably contrarius ; 
while several perfect young specimens, and one full grown, as well as numerous fragments 
of the columella of the dextral shell, have occurred. It would thus seem that the life of 
this species, so far as the seas of Britain and Belgium reveal it, exhibits the curious 
feature of having begun exclusively left-handed, then to have varied by the birth of 
