204 PLIOCENE MOLLUSCA. 



the centre one sliglitly the most prominent, with very fine lines between them ; 

 month oblong, acntely angulate above ; labial sinus deep ; canal long, narrow, 

 nearl}' straight. 



Dimensions. — L. 38 — 45 mm. B. 12 — 14 mm. 



Distribution. — Not known living. 



Fossil : Lenham Beds. Coralline Crag : Bojton, Gedgrave. 

 Waltonian : Walton-on-Naze, Beaumont, Little Oakley. Newbournian : Sutton, 

 Waldringfield, Newbourn. Butleyan : Butley, Bawdsey. 



Belgium : Diestien, zone a Isocardia cur (Casterlien), Scaldisien, Poederlien. 



Upper and Middle Miocene : Denmark, Vienna basin. Lower Pliocene : 

 Italy, Rhone Valley. Upper Pliocene : Italy — Bologna, Livorno ; France — Biot ; 

 Sicily — Altavilla. 



Remarks. — The use of the generic name Plenrotoma is now restricted to a 

 fusiform group of shells, having an elongate spire, a narrow but deep sinus more 

 or less distant from the suture, and a long, narrow and straight canal. 



In his Monograph of 1848, pt. i, p. 53, Wood described the present species 

 imder Brocchi's name of P. turricida, but in 1872, in his 1st Supplement, he 

 adopted Nyst's suggestion to call it P. turrifera, as Montagu had used the former 

 in 1803 for a well-known British shell. In 1881, however, the latter having been 

 referred to the genus Bela, Nyst reverted to Brocchi's original name, in which, 

 I think, Crag geologists may now follow him. Strictly our shell should still be 

 called P. turrifera, although it has been known throughout Europe for a hundred 

 years under the specific term of turricida. Foreign geologists have taken no notice 

 of the former name, and it would cause much and needless confusion to ask them 

 to do so now. After so long a period such unused names may be safely regarded 

 as obsolete. 



Two distinct but closely allied varieties of this species occur at Oakley and 

 elsewhere in the Anglo-Belgian Crag, the more common of the two corresponding 

 with the typical P. turricula of the Italian Pliocene. It is a slender shell, with a 

 long, narrow and straight canal, and may generally be distinguished from that 

 next to be described, although specimens of an intermediate character are some- 

 times met Avith. Most of these fossils are worn in the English Crag, and they are 

 never very abundant ; the view has therefore obtained that they are derivative in 

 the latter. In the Poederlien of Antwerp, however, they are fairly numerous and 

 beautifully perfect, having a very recent appearance, sometimes retaining the 

 colour of the spiral bands by which they are ornamented; they are generally 

 smaller and more delicate than the English shells. Wood's fig. 1 b probably 

 represents the type form. 



Specimens of P. turricula from the Miocene of the Vienna basin and of Denmark, 

 figured respectively by Homes and Dr. Ravn, have the central ridge granulate ; in 

 those from the Italian Pliocene such granulation, where present, is faint and con- 



