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 Ptipa 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 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 refiexed and very narrow ; and the tooth is 



short, perpendicular, and placed below it; whereas in Turbo 



'iiii muscorum 



