CERITHIUM. 151 



67. Cerithium vetustum, var. seminuda, Hudl. Plate VIII, fig. 7. 



1882. " Chemnitzia " vetusta, var. seminuda, Hudl. Greol. Mag., dec. ii, 



vol. ix, p. '1 49, pi. vi, fig. 13. 



Description. — This is a subulate variety, about 23 mm. in length, and with a 

 spiral angle of 14°. The spire is composed of about a dozen whorls, which are 

 flat to subconvex, increasing with perfect regularity. The subapical whorls are 

 ornamented with numerous delicate longitudinal ribs, very slightly curved. Lower 

 down this ornament becomes very faint, and expires in the body-whorl or is merely 

 represented by obscure sinuous lines. 



Base rounded and smooth ; aperture ovate : other indications wanting. 



Relations and Distribution. — Differs from G. vetustum, in being more slender 

 and in the failure of ornamentation on the anterior whorls. Rare in the Yorkshire 

 Dogger. 



68. Cerithium sdbscalariforme, D'Orb., var. spinicostata, Wright, MS. Plate VIII, 



figs. 8 a, S b, 8 c, 8 d, 

 8e,8/. 



1850. Ceeithium subscalabifoeme, D'Orb. Prod., vol. i, p. 271. 



Compare also 



1842. Melania scalaeifoemis, var. a, Desl. Mem. Soc. Linn. Norm., vol. vii, 



p. 218, pi. si, fig. 63. 

 1842. — undulata, var. b, Desl. Vol. cit., p. 217, pi. xi, figs. 59 — G2. 



Bibliography , Sfc. — This species may be regarded as the principal representa- 

 tive of the vetustum-gromp in Dorsetshire. There are, it would seem, objections 

 to both Deslongchamps' names, hence collectors usually fall back upon Cerithium 

 sub scalar if orme, D'Orb., for a set of fossils which are well known in the Bayeux- 

 beds. Although we cannot use Deslongchamps' names, we can at least apply his 

 generalizations as follows : 



" Melania undulata, var. b. Testa longiori, costis striisque frequentioribus. 

 Lias superieur." His Upper Lias I take to comprehend the Maliere (see 

 Introduction to the present Monograph), which is included in our Lower Division 

 of the Inferior Oolite. 



" Melania undulata, var. a. Testa breviori, costis et striis crassioribus 

 varioribusque. Oolite ferrugineuse" i. e. our Upper Division. 



Deslongchamps' generalisation, as above stated, holds good throughout the 

 Dorsetshire-beds, the varieties of C. sub scalarif orme having a tendency to become 



