



MADEIRAN GROUP. 189 



Helix tectiformis, Paiva, Mon. Moll. Mad. 99 (18G7) 

 var. /3. [fasciata], cingenda, Woll. 



Helix tectiformis, subvar. 2., Loive, Proc. Zool. Soc. Lond. 



192 (1854) 

 8., Paiva, I.e. 100 (1867) 

 var. y. [subfasciata], suffusa, Woll. 



Helix tectiformis, subvar. 3., Lowe, Proc. Zool. Soc. Lond. 



192 (1854) 

 „ /3., Alb., 1. c. 23. t. 4. f. 7, 8 (1854) 



„ 8. (pars), Paiva, I. c. 100 (1867) 



var. 8. [submajor, sublenticularis, semifossilis, extincta], Ludo- 

 vici, Alb. 



Helix Ludovici, Alb., Mai. Blatt. 187 (1852) 



„ Pfeiff., Mon. Eel. iii. 642 (1853) 

 „ Alb., Mai. Mad. 23. t. 4. f. 9-11 (1854) 

 „ tectiformis, a., Paiva, i.e. 100 (1867) 



Habitat Portion Sanctum, insulamque parvam adjacentem 

 ' Ilheo de Baixo ' dictam ; in aridis calcareis vulgaris. Semi- 

 fossilis (prsesertim in statu ' 8. Ludovici' 1 ) copiosissime in- 

 venitur. 



The H. tectiformis, which is .peculiar to Porto Santo and 

 the adjoining islets, is one of the most singular, though at the 

 same time most variable, land-shells of the Madeiran archi- 

 pelago ; and common as it is on the low calcareous slopes and 

 dry sandy plains of that island, as well as on the adjacent rock 

 of the Ilheo de Baixo, it appears to have been even more 

 abundant still at a former period, — it being one of the uni- 

 versal species in all the subfossiliferous deposits. On the Campo 

 de Baixo and at the Zimbral d'Areia it swarms in a subfossil 

 condition (particularly under a slightly larger and more lenti- 

 cular aspect which was described by Dr. Albers, under the title 

 of H. Ludovici, as specifically distinct), where it would seem 

 to take the place of the equally anomalous H. delphimda of 

 Madeira proper, — which is almost as plentiful in the beds near 

 Canical as the H. tectiformis is in those of Porto Santo. 



In its normal state the present Helix (which measures from 

 about 7 to 8 lines across its broadest part) is so completely 

 white, bleached, and colourless that it sometimes is not easy to 

 tell at first sight whether the examples are living or subfossi- 

 lized. But it is liable occasionally to be tinged with a livid- 

 or leaden-brown hue, — the result of two (generally indistinct) 

 fasciae below, and one above. When these bands are tolerably 

 defined, the individuals represent the ' var. /3. cingenda ' of this 

 catalogue ; but when they are suffused (the basal ones being 

 entirely confluent), so as to obscure the greater part of the 

 surface, the ' var. 7. suffusa ' is indicated. 



