Yol. 52.] OP THE CHALK EOCK. 89 



about 39°. Whorls 4 or 5 in number, convex, rather angular, the 

 posterior part of each is flat and ornamented with four longitudinal 

 rows of tubercles ; at the keel is a row of large and prominent 

 tubercles, anterior to which is a nearly flat band with faint ribbing, 

 and then three or four more longitudinal rows of tubercles. Base 

 convex, rounded, with numerous close-set longitudinal (spiral) ribs 

 bearing small tubercles. Umbilicus of moderate size. Aperture 

 sub-circular. 



Affinities. — The general form of the shell is similar to fig. 5 of 

 Eomer's 1 Delphinula tricarinata, but in that species there is 

 apparently only one row of tubercles ; the other specimens figured 

 by the same author (figs. 3, 4, and 6) are quite unlike our species. 



Portlock 2 in 1843 gave under the name of Turbo? bicarinatus 

 [Sowerby MS.] a brief description, without figures, of a very 

 imperfect specimen from the White Limestone of Tamlaght, co. 

 Derry, which is probably allied to T. Geinitzi. The name, 

 however, was already occupied, and was changed by Tate 3 in 1865 

 to Thomsoni, he at the same time referring it to the genus Pleuroto- 

 maria. The type is preserved in the Museum of Practical Geology, 

 Jermyn Street, no. |-|. It consists of three whorls ; over a con- 

 siderable part of the specimen the inner layer only of the shell is 

 present ; this gives some idea of the original form of the whorls, 

 justifying Portlock's statement that they have ' two slight parallel, 

 rather distant ridges winding up below their middle.' Adjoining 

 the suture of the last preserved whorl is a very small fragment of 

 the outer layer of the shell showing the ornamentation : this is 

 much less coarse than in the Chalk Eock species. I have not been 

 able to obtain another specimen from the White Limestone ; and 

 until this is done the characters of the Irish species and its relation 

 to T. Geinitzi cannot be made out. 



Distribution. — Chalk Eock of Dover, Cuckhamsley, Hitchin, and 

 Luton. 



Turbo gemmatus, Sowerby. (PI. IY. figs. 9 & 10.) 



1850. Turbo gemmatus, J. de C. Sowerby, in F. Dixon's 'Geol. Sussex,' p. 349 

 (p. 385, ed. 2, 1878), pi. xxvii. f. 26, 33 ; 1854. J. Morris, ' Cat. Brit. Foss.' ed. 2, 

 p. 283. 



1878. Turbo Seberti, C. Barrois and J. de Guerne, Ann. Soc. geol. du Nord, 

 vol. v. p. 58, pi. iii. f. 11 ; 1887. A. Peron, ' Notes pour servir a "Hist, du Terr, de 

 Craie,' Bull. Soc. Sci. hist, et nat. de l'Yonne, ser. 3, vol. xii. p. 142, pi. i. f. 5-8. 



[Non T. gemmatus, Lycett, Quart. Journ. Geol. Soc. vol. xiv. (1853) p. 342, 

 pi. xiv. f. 7, from the Inferior Oolite.] 



Description. — Shell conical, slightly longer than broad, composed 

 of six whorls which are a little convex, and ornamented with 

 several (generally seven) longitudinal ribs bearing granules — those 

 on the upper rib being larger than the others. Sutures well marked. 

 Margin of the last whorl rounded ; base slightly convex ; umbilicus 

 large with a ridged margin. Aperture subquadrangular or rounded. 



1 F. A. Eomer, 'Die Verstein. des norddeutsch. Kreidegeb.' 1841, p. 81, 

 pi. xii. f. 3-6. 



2 ' Eeport on the Geology of Londonderry, etc' p. 421. 



3 Quart. Journ. Geol. Soc. vol. xxi. p. 37. 



