1 10 GREY CHALK MARL. 



Locality. Hamsey. 

 20. Trochus linearis, tab. xviii. fig. 17. 



Conical, wreaths slightly convex, transversely striated, with a prominent 

 line along the centre and base of each volution ; base flat ; umbiHcus 

 obscured by the last volution ; aperture transversely depressed. 



In figure 17, the linear markings, by which this species is distinguished, 

 are but obscurely shown ; but in a specimen subsequently discovered, and 

 which contains a portion of the original shell, these characters are strongly 

 marked. 



Localities. Hamsey, Middleham. 



21. Trochus, tab. xviii. fig. 16. 



The cast of a species of trochus of an oval form; probably of T. linearis, 

 distorted by compression. 



Locality. Hamsey, Middleham. 



22. Auricvila incrassata, tab. xix. figs. 2, 3. 34. 



Ovate, ventricose, transversely sulcated ; sulci longitudinally striated ; 

 spire short ; columella triphcated ; outer lip thick, with a broad trans- 

 versely striated border. 



The three folds on the columella, the striated sulci, and the broad 

 band on the margin of the external Hp, are the distinguishing marks of 

 this beautiful shell. It is a small species, consisting of about three volu- 

 tions, and seldom exceeds half an inch in length, by OS inch in width. 

 The spire is short, the outer lip thick ; the broad striated band gives 

 a peculiar feature to the back of the shell. The striae which cross the 

 delicate grooves or svdci, are so minute, as scarcely to be visible to the 

 naked eye. When viewed with a lens they appear elevated and sharp, 

 dividing the furrows into minute rectangular cells. This species occurs 

 silicified in the Blackdown whetstone pits of Devonshire, and is described 

 by Mr. Parkinson. ]Mr. Sowerby mentions that " it resembles A. ri?igens 

 of Lamarck, but the want of striae within the outer hp, and the presence 

 of longitudinal striae upon the surface, distinguish the British shell." 



Fig. 2. is an elegant specimen, in which the shell is replaced by a thin 

 pellicle of reddish brown sulphuret of iron, upon a cast of indurated marl. 



