90 
THE GEOLOGIST. 
and ribs become not only actually, but relatively much more numerous as the shell 
enlarges ; they are crossed horizontally by a number of (about ten) fine spiral strise. 
The base makes a right angle with the spire, as in many recent species it is prolonged 
much in front of the side of the whorl. 
This form nearly resembles C. ornatissimum, Desh,, and is possibly 
its lineal representative. The differences of ornamentation are such as 
constantly are produced by the conditions of existence. The unequal 
spiral rows of tubercles of C. ornatissimum become iu this form equal, 
and pass round the spire contiguous, so as to conceal the suture. In 
this form the excessive multiplication of the elongated tubercles of 
the anterior row tends in the last whorl to make that row less dis- 
tinct ; a similar character is also to be noticed in the adult of tlie 
French species. The longitudinal ribs of this variety exist in the 
species from the Gault only as strise. The basal prolongation of the 
lip is, however, a feature in the chalk-marl form which will keep the 
two varieties from being confounded. 
A second slight variation is met with not rarely in the lower argil- 
laceous chalk of Burwell, in Cambridgeshire. It more closely resem- 
bles the foreign type than the BrightiDn specimen. In it the posterior 
row of tubercles is placed on an elevated rib ; while the anterior row, 
at least on the anterior half of the shell, is wanting, being represented 
by rather elongated thickenings of anterior ends of the very fine 
striae which replace the longitudinal ribs. — {Wooclivardian Museum.) 
CliRITHIUM. 
A very elongated cone, three times as high as wide. Rather few whorled; whorls flat, more 
than twice as wide as high. Each whorl is ornamented with three spiral rows of rather 
small, sharp tubercles, about twelve to fourteen on a whorl in each row. The tubercles 
are so placed as to form rows nearly perpendicular, or rather parallel to the labial side of 
the spire. Throughout the shell the spiral rows are at equal distances apart. 
Cerithium Gallicum (D'OrJ.), var. 
A greatly elongated cone, three times as high as wide, many- (about 12-) whorled; 
whorls inflated, with an elevated mesial angle, from which they become smaller anteriorly 
and posteriorly, towards the sutures ; the posterior half of each whorl is flat, but the 
anterior half is slightly convex. The posterior sutural margin is bordered by an elevated 
rib, which bears a numerous row of closely-placed tubercles. The part of the whorl 
between the suture and the suture-like anterior margin of this rib is nearly four times as 
wide as high ; the whorl is one-third as high as wide. A row of sharp, elevated tubercles 
surmounts the mesial angle of the whorl. The whole spire is finely cancellated, the 
longitudinal strise being stronger than those transverse. The base is convex, and sepa- 
rated from the whorl by a slight angular inflation. — ( Woodwardian Museum) 
This differs from the French form chiefly in the small size and 
number of tubercles on the mesial angle, and is what some authors 
would regard as a representative species. 
Pleurotoma amphiloga (n. sp.). 
Shell elongated, 5- or 6-whorled ; spire much elevated, two and a half times as high 
as wide, turreted ; whorls elevated, nearly as high as wide, sides parallel with the sutural 
shoulder rounded. The whorls are ornamented with moderately elevated, narrow, longi- 
tudinal ribs, which increase in number, though not in size or closeness, with the growth 
