54 SUPPLEMENT TO THE CRAG MOLLUSCA. 



determination. The late Dr. S. P. Woodward obtained a somewhat corresponding 

 specimen from the Cor. Crag of the Orford neighbourhood, which has the aperture 

 rather more perfect than my own ; and I am now enabled with the two fragments to give 

 a probable representation for a species. Dr. Woodward's specimen was accompanied 

 with the name of Mesalia polaris. I have carefully compared these fragments with that 

 species, and I think that they are quite distinct from it. The sculpture of polaris shows 

 four or five broad threads in a spiral direction, with corresponding spaces between them, 

 whereas the Cor. Crag shell is covered with numerous fine threads and narrow depressions. 

 I have placed it provisionally in the above-named genus, which I think it more nearly 

 resembles than that of Mesalia ; the shells of this latter genus have a somewhat emargi- 

 n ate base, or rather a reflexion of the lower part of the inner lip, which the Crag shell 

 does not appear to possess. 



Turritella planispira, S. Wood. Crag Moll., vol. i, p. 76. Tab. IX, fig. 11. 



M. Mayer in ' Jonrn. de Conch.,' vol. xiv, p. 173, PI. Ill, fig. 2, has described a 

 species of Turritella, with the specific name of Sandbergeri, and to this he has given as a 

 synonym, T. planispira, S. Wood, non Nyst. All the Coralline Crag forms of this 

 genus possess a wide range of variation in the external ornament, but I believe my species 

 T. planispira forms a group as well defined and constant as any. 



It has been identified with subangulata of Brocchi by Mr. Jeffreys ('Quart. Journ. 

 Geol. Soc.,' vol. xxvii, p. 146), but I think it is not that shell, as it agrees with it neither 

 in the form of the whorls (which are invariably flat, and not subangular), nor in the 

 external sculpturing. The figure of it in Tab. IX of ' Crag Moll.,' shows only six or 

 seven spiral threads, but it has always eight, and more frequently nine, all of equal size. 

 In some individuals the central thread thickens, and so produces a faint subangulation, 

 which is scarcely perceptible without a magnifier. This shell, and that called T. incras- 

 sata var. bicincta (fig. Id of Tab. IX of ' Crag. Moll.'), appear to me to constitute 

 the most marked forms of this genus that lived in the Cor. Crag sea ; but 

 inasmuch as a series may be selected, showing a gradation of all the forms into each 

 other, I doubt whether the whole of the Coralline Crag varieties and species, triplicata, 

 vermicularis, bicincta, and planispira, are not merely individual and inconstant variations 

 of the one species incrassata ; and the same remark might be applied to Brocchi's species, 

 duplicata, bicarinala, subangulata, marginata, and replicata. 



Before dismissing the genus Turritella, I may mention that Mr. Busk in his beautiful 

 'Monograph of the Crag Polyzoa/ at p. 59, gives Cellepora edax, " habitat Cor. Crag, 

 S. Wood, on a specimen of Natica and Turritella." 



The living analogue found by the Rev. Mr. Hinks on the coast of Devonshire, was 

 attached to a Turritella, but the late Mr. Alder told me he had a specimen of C. edase upon 



