60 J. S. GARDNER ON THE CRETACEOUS LENTALIID^!. 



tab. 79. f. 5) from a small fragment of an internal cast without 

 markings of any sort ; and what is visible of it presents no direct 

 evidence as to whether it was striated or not. Mounted on the 

 same tablet with the figured specimens are others found subsequently, 

 both smooth and striated. Sowerby was evidently unaware, at the 

 time he wrote his first description of the species, that there were 

 more species than one in the Blackdown beds ; the size of the 

 original specimen, however, indicates it to be the striated species, 

 the smooth being smaller and more slender. Setting the original 

 figure aside, there are excellent engravings of the striated species, by 

 J. de C. Sowerby, in the Trans. Geol. Soc. 2nd ser. vol. iv. pi. 18, 

 p. 343. De Byckholt, who had never seen the actual specimens, states 

 that D. medium has no longitudinal striae, but is covered with promi- 

 nent folds of growth. Geinitz, Reuss, and Pictet have fallen into 

 the same error. The synonymy of foreign writers cannot be unravelled 

 without comparison of the actual specimens. 



This shell appears to be very abundant at Blackdown. Dr. Gwyn 

 Jeffreys has kindly shown me specimens of D. capillosum, a deep-sea 

 form, which bears some resemblance to this species. 



Dentalium divisiense, sp. nov. Upper Greensand. (Plate III. 

 fig. 15.) 



Shell very gradually tapering, extremely slender and elongate, 

 slightly curved : sculpture, from 20 to 25 even, slightly flexuous ribs 

 extending from the apex to the aperture without any apparent 

 increase in their number. L. 3 # 125 in. B. *2 in. 



The specimen, which is distinguished by its long and slender 

 aspect, is from Devizes. It is now in the Jermyn-Street Museum, 

 and remains unique. 



Dentaliuh alattjm, sp. nov. Gault. (Plate III. figs. 16-20.) 



Shell moderately curved, elliptical externally, cylindrical inter- 

 nally ; thin at aperture, becoming very thick at apex ; laterally 

 keeled ; ribbed longitudinally and decussated ; growth irregular 

 and uneven. L. 2*75 in. Width of cylinder only at aperture '25 in. 



The cylindrical tube of this shell is bordered in its entire length 

 with two lateral flanges or flattened ledge-like expansions, each 

 about half the diameter of the cylinder and least prominent near 

 the aperture. These flanges readily become detached and leave a 

 groove-like scar (fig. 18). The surface of the shell is ribbed, and 

 decussated by fine transverse striae, which are more closely set and 

 less prominent near the aperture. The ribs are a little finer and 

 closer together than in D. decussatum, the ribs of which they re- 

 semble in arrangement ; they usually die away near the aperture, 

 leaving about a fourth part of the shell nearly smooth. 



The species is not uncommon in the Gault at Folkestone, but has 

 been hitherto overlooked by collectors. 



The lateral thickening, present in the species just described and 

 in many described on the Continent, is most developed in B. alatum. 

 The only existing species which is at all keeled is a much smaller 



