J. S. GARDNER ON THE CRETACEOUS DENTALIID.E. 57 



The second group, B, comprises only smaller and comparatively 

 smooth forms. In this group three species are described: two 

 are new ; and one is redescribed, viz. D. cylindricum, Sowerby. 

 There is no doubt that many others exist and may be added at 

 a future time. D. cylindricum is only known in England from 

 Blackdown ; and its history is curious. Under this name Sowerby 

 described, in the ' Mineral Conchology,' vol. i. tab. 79. f. 2, 

 p. 179, a group of Ditrupa plana in ochreous earth from the 

 Eocene at Emsworth. By an accident Emsworth was printed 

 Exmouth ; and the fossils have therefore ever since been supposed 

 to be of Cretaceous age. In Sowerby's tables of fossils in Eitton, 

 ' Geological Transactions,' 2nd ser. vol. iv. pp. 240 and 364, the error 

 is repeated. Instead of rejecting the name as a synonym of Ditrupa 

 plana, it is applied to the smooth Blackdown form, to which in collec- 

 tions this name is generally seen attached. A second species, more 

 or less regularly ringed, is abundant in the Gault, and has been 

 named D. Jeffreysi in compliment to Dr. Gwyn Jeffreys, to whom 

 I am under obligations for assistance in the preparation of these 

 descriptions. The third species is new and very distinct, possessing 

 the small, needle-like aspect described by Deshayes as characterizing 

 D. acicula of the Eocene ; it is named D. acuminatum. Besides 

 these Mr. Baily has described a fourth species, D. cartatulum, from 

 the Upper Greensand of Aberdeenshire * ; but this I have not seen. 



The next genus, Entalis, is represented by a unique specimen 

 which was detected by that excellent observer Mr. Meyer among 

 the common Dentalium cylindricum of the Blackdown beds. It is 

 not unlikely that other specimens exist, unknown to the owners, in 

 the numerous collections from this locality ; and I would therefore 

 call their especial attention to the fact that, although of the same 

 size as D. cylindricum, it is perfectly smooth and of an even texture, 

 whilst the former is rugged and ringed by lines of growth, the fissure 

 being besides very distinct, long, narrow, and reaching J the entire 

 length of the shell. Even where, as generally happens, the slender 

 end of Dentalium is broken off or not sufficiently cleaned from the 

 matrix, the smooth texture should call attention to it. None of the 

 Gault forms are fissured, as I have convinced myself by an examina- 

 tion of over 300 specimens. 



The genus Siphodentalium, to which at present only two species 

 are here referred, will probably soon be enlarged. It is but quite 

 recently I have found specimens in the Cretaceous clays ; and further 

 investigation will no doubt add to our knowledge. Both the species 

 resemble iS. quinqaangulare of Eorbes, and more nearly S. tetragonum 

 of Brocchi. 



The genus Cadulus is represented by a minute species of about 

 the size of Cadulus subfusiformis, Gwyn Jeffreys, which is remark- 

 able as being the first described from rocks so old as the Cretaceous 

 in Europe. A species has been described from rocks supposed to be 

 Cretaceous, in California. The method of growth of this shell is 

 not very apparent. So far as I am aware, the young shells of 



* Quart. Journ. Geol. Soc. vol. xiii. p. 87, pi. ii. fig- 8. 



