426 PLIOCENE MOLLUSCA. 



and strong tuberculation where they intersect, but are never varicose; there are three 

 spiral rows on the lower whorls, the centre row becoming smaller and squeezed 

 out on the upper ones, the base of the shell being rounded and spirally ridged ; 

 suture slight, narrowly channelled ; mouth sub-quadrangular; labial groove narrow, 

 turning to the right ; inner lip broad, forming a thick pad on the pillar. 



Dimensions. — L. 8 — 12 mm. B. 2 — 3 mm. 



Distribution. — Recent : southern and western coasts of England and Wales, 

 Ireland, Scotland from the Clyde to the Shetland Isles, Norwegian coast, Brittany 

 to Madeira and the Canaries; generally diffused in the Mediterranean, Adriatic 

 and iEgean ; Morea, Egypt; west coast of N. America (Jeffreys). 



Fossil: St. Erth. Gedgravian Crag: Gedgrave, Sutton. Wal- 

 tonian : Walton-on-Naze, Little Oakley. 



Pleistocene : Garvel Park, Cumbrae, Largo, Shewalton. 



Holocene : Portrush. 



Oligocene : Denmark, northern Germany ? 



Miocene : Italy (Elveziano, Tortoniano). Vienna basin. South-west France. 



Lower Pliocene : northern Italy — many localities. Normandy, Biot. 



Upper Pliocene : Asti, Bologna, Orciano, Legoli, Monte Mario. Sicily — Alta- 

 villa, Messina. Belgium — Scaldisien : Antwerp. 



Pleistocene : Italy — Reggio, Taranto, Livorno, Valle Biaia. Sicily — Messina, 

 Monte Pellegrino. Christiania fiord, Tapes-hanks. 



Remarks. — There are two forms of the present shell, originally regarded as 

 specifically distinct, but now generally held to be varieties of our species. The 

 one, T. perversus, Linne, is much the larger, sometimes exceeding 30 mm. in length. 

 This is figured under that name as recent by MM. Bucquoy and his colleagues 

 (op. cit.), and as fossil by Prof. Sacco and Sign. Cerulli-Irelli (op. cit.). It is 

 typically southern, and does not occur, so far as I know, either living in British 

 seas or in the Anglo-Belgian Pliocene. The other, T. adversa, is much smaller, 

 from 8 mm. long, has a northern range, and is that found recent on the coasts 

 of Great Britain, and fossil in the Crag and in the Pleistocene ^Vi^cs-banks of 

 Norway. It is figured, however, as recent in the Mediterranean, and fossil in the 

 Upper Pliocene of Italy, but under the name of T. perversa var. adversa, which I 

 think correctly describes it. 1 Jeffreys says, " I can see no other difference than 

 that of size between Mediterranean and British specimens." 



Our shell was only known as a fossil to Wood from the Coralline Crag, but has 

 been found since by Prof. Kendall at Walton, by myself at Oakley, by M. Dollfus 

 in Normandy, and by Mr. Bell at St. Erth. 



A nearly allied species from the Oligocene of north Germany and Denmark is 

 described by Prof, von Koenen and others under the name of Triforis Fritschi. 



1 Tbe Conchological Society of Great Britain has adopted the name T. perversa for the small 

 British variety. 



