154 TESTACEA ATLANTICA. 



consors, its basal volution is less constricted at the aperture, 

 and the minute and sharply defined granules with which it is 

 everywhere beset (both above and below), and which constitute 

 its most peculiar feature, will still further tend to distinguish it. 



Helix compacta, 



Helix compacta, Lowe, Cambr. Phil. S. Traits, iv. 50. t. 6. 



f. 2 (1831) 



Pfei/., Mon. Hel. i. 198 (1848) 



Lowe, Proc. Zool. Soc. Lond. 184 (1854) 



(pars), Alb., Mai. Mad. 41. t. 10. f. 15-18 



(1854) 

 Paiva, Mon. Moll. Mad. 40 (1867) 



Habitat Maderam, Portum Sanctum, et (sec. Paiva) Deser- 

 tam Australem ; in Portu Sancto vulgatissima, sed in Madera 

 promontorium ' Sao Lourenpo ' tantum colens. Semifossilis, et 

 in Madera et in Portu Sancto, abundat. 



This is a little Helix which attains its maximum in Porto 

 Santo, in which island it is both general and abundant ; never- 

 theless it exists also on the Ponta de Sao Lourenco of Madeira 

 proper, the low rocky promontory which stretches out to the 

 eastward and which has many features in common not only 

 with Porto Santo but likewise with the Desertas, combining, 

 as it were, to a certain limited extent, the faunas of the three 

 compartments of the Group. The Baron Paiva cites, also, the 

 H. compacta from the Southern Deserta, which is not an 

 unlikely locality, though I have no means of testing its accuracy. 



In a subfossil condition the H. compacta abounds throughout 

 the calcareous deposits of Porto Santo ; and it is likewise com- 

 mon at Canical, where some of the specimens (which represent 

 the ' var. /3. 'major 9 of Lowe) are of a slightly larger size and 

 possess more the characters (so far as one is able to judge from 

 examples which are both colourless and superficially decomposed; 

 of the H. consors. 



Although variable in size and sculpture, the H. compacta 

 may be regarded normally as being a good deal roughened 

 above, both with costate lines and granules, but smoother and 

 comparatively unsculptured beneath, the lines being there 

 lighter and finer, and the granules obsolete. In the Madeiran 

 examples (i.e. from Point Sao Lourenpo) the striae and granules 

 are less coarse than in the ordinary Porto-Santan ones, and the 

 spire is just appreciably less depressed. These were considered 

 as typical by Mr. Lowe, by whom they were first detected, 

 about the Piedade and the fossil-bed, during April and May of 

 1827. The Porto-Santan ones however (which correspond with 



