154 Rev. R. SHEPPARD s Account 
having three of the middle volutions vastly more prominent than 
the rest, and widely separated from each other. 
20. TURBO TRIDENS. Trans.Linn. Soc. vol. viii. p. 181. 
This rare and interesting species had hitherto been confined 
to a single habitat, viz. Amersham wood in Buckinghamshire ; a 
specimen procured from which place I owe to the kind attention 
of my learned and worthy friend Dr. Goodall, Provost of Eton ; 
but on the last day of May 1821, myself and son went on a 
conchological expedition to Friston wood, and in a space not 
exceeding fifteen feet square (where we were employed on our 
knees nearly two hours), under moss kept moist and shaded by a 
luxuriant growth of Dog’s Mercury and thick underwood, we 
_ were fortunate enough to find twenty-four specimens. One of 
them had only two teeth, that on the lip being wanting, it pro- 
bably being the last tooth formed. Young shells have the aper- 
ture narrow, acuminated, and without teeth ; but there is a fold 
upon the columella. I have since procured thirty- eight specimens 
from the same spot. 
It forms a subdivision of the genus Turbo, agreeing neither 
with the Clausilia nor Pupa of Draparnaud. It is scarcely ne- 
cessary to add, that the Pupa tridens of that author is a very 
different shell. 
As Dr. Pulteney says that T. tridens is white, and found o on 
water-plants, Iconclude his specimens to have been bleached, and 
conveyed from their natural situation by the waters of a flood. 
23. TURBO MARGINATUS. 
Pupa marginata, Draparn. 
This species is dark-brown and sub-opake ; the margin of the 
aperture is slightly reflexed and very narrow ; and the tooth is 
short, — and placed below it; whereas in Turbo 
muscorum 
