J. S. GARDNER ON THE CRETACEOUS DENTALIIMI. 61 



deep-sea form, described by Dr. Gwyn Jeffreys as D. ensiculus ; but 

 this differs most essentially from ours, being neither cylindrical 

 internally nor ribbed. 



Since writing the above I have found a slightly alate form 

 nearly 5 inches in length to be not uncommon in the Grey Chalk of 

 Dover. This I have named D. majus. 



Group B. 



Dentalifm cylindrictjm, Sby. BlacMown Beds. (Plate III. figs. 

 21-25.) 



Shell cylindrical or elliptical, slender, elongated, moderately 

 curved, thickened laterally, rugose with irregular varices and lines 

 of growth, occasionally exhibiting an imbricated structure ; aper- 

 ture circular, margin thin; apex minute, entire. L. *9583 in. 

 B. -0111 in. 



This species has a clumsier appearance than D. glabrum, being 

 thicker and more rugose, and appears to be specifically distinct, 

 even after making allowance for the difference of matrix, the condi- 

 tion of mineralization, and the fact that the apex is seldom preserved. 

 The uneven growth may be partly due to its sandy habitat when 

 living ; but the appearance cannot be ascribed to the condition of 

 mineralization of the specimens, as Entalis Meyeri, from the same 

 beds, is smooth. 



It is difficult to realize that Sowerby was unacquainted with this 

 form, as it is so abundant at Blackdown ; but it does not appear in 

 the ' Mineral Conchology,' the name being in that work applied to 

 Ditrupa plana from Emsworth, by a mistake printed Exmouth. 

 The mistake has been repeated in Sowerby's later works ; and D. 

 cylindricum does not appear in his lists of fossils from Blackdown 

 in the Geol. Trans. 2nd ser. vol. iv., but only as being from Ex- 

 mouth. I have here transferred the name to the Blackdown fossils, 

 as it has been for a long time almost universally applied to them. 



Dentalium Jefereysi, sp. nov. Gault. (Plate III. figs. 26-33.) 



Shell cylindrical or very slightly elliptical, slender and elongated, 

 moderately curved, thin, smooth and polished : surface marked in 

 places by lines of growth, transversely ringed throughout or towards 

 the apex only. Length of the largest specimen 1*50 in., breadth 

 •125. 



The Gault shells are usually crushed and pressed into one or more 

 folds, giving them an irregularly grooved appearance, the grooves 

 not usually extending the whole length of the shell. Owing to 

 this crushing few specimens show the form of the tube ; but it is 

 cylindrical or very slightly flattened. The closely set rings cannot 

 be observed without the aid of a lens, but are then seen to be 

 rounded and extremely regular, sometimes present throughout the 

 whole length of the shell. Dr. Gwyn Jeffreys has shown me 

 similarly ornamented and undescribed specimens from the Bay of 

 Biscay. 



