LAURIA, SUBGENUS LEIOSTYLA. 67 



L. tabularis appears to have a shorter angular lamella than 

 usual in cylindracca. See also under L. dadion. 



Subgenus Leiostyla Lowe. 



Leiostyla Lowe, Ann. Mag. N. H. (2), ix, April 1852, p. 

 276, for P. vincta, irrigua, laurinia, laevigata, recta, maci- 

 Imta; P. Z. S., 1854, p. 208, "type P. anglica Fer. "—Liostyla 

 Lowe, v. Martens, Die Heliceen, 1860, p. 293. 



Alvearella Lowe, Ann. Mag. (2), ix, 1852, p. 277; P. Z. S., 

 1854, p. 212, P. cassidula designated type. 



Charadrobia Albers, Malacographie Maderensis, 1854, p. 

 63. — v. Martens, Die Heliceen, p. 293, type Pupa cheilogona 

 Lwe. 



Caucasica Caziot et Margier, Bull. Soc. Zool. France, xxxiv, 

 1909, p. 141 ; P. caucasica type by tautonymy. 



The shell has, in addition to the deeply entering angular 

 and columellar lamellae of Lauria. proper, a parietal lamella 

 and one or more palatal folds. Immature (neanic) stage hav- 

 ing angular and columellar lamella?, usually also a parietal; 

 radial teeth in the base as in Lauria proper. The animal is 

 oviparous. 



Type L. vincta (Lowe). Distribution, islands of the At- 

 lantic, western Europe, Caucasus region. 



Leiostyla, like Lauria- proper, is markedly discontinuous in 

 distribution, the colonies in the British Islands, Portugal, 

 Algeria, the Caucasus region and the islands of the Atlantic 

 are all of small area and are completely isolated. The assem- 

 blages of Madeira and the Caucasus may be traceable to more 

 than one migration, or in other words, may have descended 

 from more than one ancestral stock for each, but this can only 

 be demonstrated by further discoveries in the Tertiary. At 

 present there seems no conclusive evidence that either the 

 Caucasian or the Madeiran series is di- or polyphyletic, as all 

 of the Tertiary species (possibly excepting L. minax) belong 

 to the typical L. anglica group of Leiostyla. The L. cheilogona 

 group is probably the most primitive of the Madeirans, being 

 very close to Tertiary species of Europe, to the Recent British 

 species, and to such Caucasian forms as L. tenuimarginata. 



Part of the Madeiran species agree closely with the Euro- 



