GREY CHALK MARL. 125 



length ; and one found by the author, at Middleham, is of much larger 

 dimensions. 



A row of from fifteen to sixteen obtuse rounded tubercles, are disposed 

 round each volution, at about one-third from the superior margin, and 

 beneath these are placed three sets of smaller tubercles. The inferior 

 surface of the whorls is marked with radiating costae, that terminate in 

 the lowermost row of tubercles. The siphunculus is placed midway 

 between the larger projections, and the upper edge of the wreaths, which 

 is impressed by the ribs of the preceding volution. The base of the aper- 

 ture is contracted, and the tubercles on the body of the last whorl are 

 elongated, forming irregular tubercular costee, which are reflected towards 

 the aperture. 



Tlie fossil discovered by De Montfort " appears to have been in such 

 a state of perfection, as to allow of its form being made out completely. 

 It is regularly formed into a spire, the whorls of which are projecting and 

 articulated, the foUaceous sutures produced by the edge of the septa being 

 apparent. The opening of the shell is nearly round ; the columella flat 

 without any folds ; and the septa perforated nearly in the centre, by a 

 syphon*." 



The magnificent British specimen of this species, previously alluded to, 

 was found in a bank of marl, near the mansion of the Kev. J. Constable, 

 at Middleham, in the parish of Ringmer. It is a cast of indurated marl 

 of an ochraceous colour, retaining in one part a thin iridescent pellicle of 

 the pearly coat of the shell. Six volutions remain, the largest of which is 

 five inches and a half in diameter. Upon a moderate calculation, the 

 original, when perfect, must have exceeded two feet in length. The 

 siphunculus is exhibited on the three upper volutions f. 



Tab. xxiv. fig. 7. A remarkably fine cast from Middleham. 



The siphunculus, shewn in the three upper volutions, does not exist 

 in the specimen, but is introduced here that the subject may be more 

 fully illustrated. 



* Organic Remains, Vol. iii. page 147. 

 -f- This specimen is figured in Sowerby's Mineral Conchology, tab. Ixxiv. 



