LITTOKINA CASSIUS. 85 



Genus LITTORINA, Ferussac. 



As the presence or absence of a pearly layer fails as a criterion between Littorma 

 and Turbo in Jurassic rocks, the employment of either term must not be considered 

 as stating anything upon that point, except that no differentiation into two layers 

 of different character has been observed. Turbo, however, is also characterised by 

 having a calcareous operculum. Such opercula would not more easily perish, I 

 suppose, than the shell, for Ave have examples, as in Euomphalus and Nerita, in 

 which they are preserved. Absence of opercula from the beds where the shells in 

 question are abundant is as good a proof as we can desire that they are not Turbines. 

 We must adopt, therefore, other names than Turbo for turbine-like shells if we 

 would use exactness. 1 Littorinse are compact shells and the aperture is affected 

 somewhat by the preceding whorl. 



Littorina cassius (D'Orbigny). Plate VIII, fig. 11. 



1855. Turbo cassius, D'Orbigny, Pal. Franc. Terr. Jurassiques, vol. ii, p. 350, pi. cxxxiv, figs. 1, 3. 



Type. — " Shell oval, conic, slightly umbilicated, spire regular, composed of 

 slightly convex whorls provided with 4 longitudinal [spiral] ribs formed by hollow 

 tubercles, elevated and imbricated. The last whorl has 11 similar ribs of smaller 

 and smaller size. Mouth round, thickened in the columellar region. Length 

 15 mm." From the white limestone of Langrune and Luc. 



Description. — The single specimen in hand is of the right size and shape, having 

 a spiral angle of 62°. In the uniformity of the ribbing throughout and in the 

 number of ribs or rows of tubercles in the upper whorls it also agrees. According 

 to the description it should have a slight umbilicus ; it has at most the feeblest 

 umbilical slit, but more so than the figure. There should be 11 ribs in all on the 

 last whorl, and it has at most 9. The tubercles should be hollow, and they arc so 

 filled or covered with matrix that this character cannot be determined — the shell 

 being the softer — but one or two appear to be excavated towards the aperture. 

 This specimen is from Scarborough. 



Relations. — This is not the same specimen but appears to be of the same species 

 as that figured by Eudleston as Turbo funiculatus, though the angle as drawn is 

 larger. The base and aperture are not seen in that fossil, and the ornament and 

 shape do not seem to agree with the Corallian shell as figured in 1881. Our shell 

 differs from /,. davousti (I)'Orb.) in the spiral angle, coarseness of ornament, and 

 umbilicus. 



1 See remarks by Hudleston to the same effect (' Geol. Mag.' [2], vol. viii, p. 52). In his ' Memoir 

 on the Gasteropoda of the Inferior Oolite ' Turbo lias almost disappeared. 



