178 
This magnificent shell lias long' been a favorite 
amongst collectors, but its fibrous structure renders it so 
fragile that it is very seldom found perfect, fragments 
and young individuals are very common at i lord well, as 
well as in the cotemporaneous formation near Paris. It 
has also been found at Highgate, see tab. 30, sometimes 
imbedded in septaria. The variety /3 is by no means 
common, I have seen but one good specimen of it ; it 
enhances the value of a fine collection of Hordwell Fossils 
belonging to my kind Friend Miss Dent, along . with that 
from which the large figure upon tab. 298 is taken. The 
sinus in the lip of this variety is the more curious, since 
such an occurrence when constant would form a generic 
character as in Pleurotoma. 
Tab. 298 shews the young state at fig. 1, 2, and 3 ; 
fig. 4 is from a fragment exhibiting a back view of the 
reflected canal, and the dotted outline indicates the size 
of the largest specimen in Miss Beminster’s collection. 
Tab. 300 is from one kindly lent me by the Rev, John 
Ireland,* in it the canal is not reflected over the spire. 
As the shell grows old it increases more in thickness 
than in size, therefore it is not fair to judge, as Monitor! 
would do, of the size by the comparative thickness of 
fragments, for the lips of full grown shells are often very 
thin. The var (3 might be confounded with Rostellaria 
Columbaria, of which I have given a figure among 
my miscellaneous plates, which will often be found useful 
for references, but the canal and winglike lip are 
very different in form and proportion : in R. columbaria the 
lip is narrowest at the lower part and rather triangular* 
and the canal perfectly simple, free from the additional 
swelling described above; it is also a much smaller 
shell. 
* This Gentleman's name has formerly been erroneously given Jur.AMo a 
for which I beg to apologize. 
