124 GREY CHALK MARL. 



to seven inches in circumference, and from three to five inches long; the 

 lowermost volution is but rarely preserved, and no traces of the shell 

 remain. 



Tab. xxiii. fig. 15, represents a specimen with part of the lowermost 

 volution. 



Tab. xxiv. figs. 1, 4, 5, exhibit the usual varieties of this species : in 

 figures 4 and 5, the union of the ribs with the tubercles is distinctly 

 shewn. 



LocaHties. Hamsey, Clayton. 



43. 'Turr'Aites undulatus. Tab. xxiv. fig. 8, Tab. xxiii. figs. 14. 16. 

 Volutions reversed, ornamented with prominent transverse costas. 

 This species was first noticed and described by the author. It is 



characterized by its prominent transverse costee, which are undulated in 

 some examples, and extend directly across the whorls in others. In 

 many specimens the ribs are oblique, and somewhat tubercular, a circum- 

 stance that has led some naturahsts to question the correctness of con- 

 sidering the present species as distinct from T. costatus. In the casts of 

 the adult shell, the characters of the two species are however distinctly 

 marked, and leave no doubt of the propriety of their separation. 



The Turrilites undulatus attains a larger size than the preceding, some- 

 times exceeding three inches in diameter. 



Tab. xxiv. fig. 8, represents a very perfect example. It consists of 

 eight volutions, including the lowermost, and exhibits the rounded base 

 of the columella. On the opposite side, the siphunculus, fiUed with 

 sulphuret of iron, is beautifully shewn. To my brother, Mr. Joshua 

 Mantell, whose kindness I have had repeated occasions to acknowledge, 

 I am indebted for the possession of this interesting specimen. 



Locality. Hamsey. 



44. Turrilites tuberculatus. Tab. xxiv. figs. 2, 3, 6, 7. 



Volutions reversed, beset with a longitudinal row of nodular projec- 

 tions, beneath which are three rows of tubercles; inferior surface of the 

 wreaths radiated. 



This species is the largest of the genus. De Montfort mentions 

 a specimen found at Rouen, which measured nearly a foot and a half in 



