502 TEST ACE A ATLANTIC A. 



his ' Malacographia Maderensis,' figures a shell as the H. ad- 

 vena, from a unique example which was found by Hartung in 

 Porto Santo ; but, whatever species it may represent, it cer- 

 tainly has nothing whatever to do with our present one from 

 the Cape Verdes. 



The H. advena belongs to exactly the same type as the H. 

 Visgeriana and serta (both, likewise, from the Cape Verdes), 

 and differs from all the numerous forms of the Madeiran H. 

 erubescens in its surface being more shining and totally unmal- 

 leated, but with nevertheless the oblique transverse striae, much 

 more coarsely and regularly developed. Its spire, too, is appre- 

 ciably more obtuse, or less elevated; its aperture is a trifle 

 rounder, and relatively not quite so large ; its peristome (which 

 has the upper portion somewhat less deflected) is not quite so 

 expanded or recurved ; and its umbilicus is not always so com- 

 pletely closed over. Added to which, the colour in the H. 

 advena is different, there being scarcely any rosy tint n any 

 part of the surface, but more or less of a faint blueish or leaden 

 one, which although now and then obscure is seldom entirely 

 absent. The fasciae seem very variable, but are often broad, 

 dark-brown, and (although normally four in number) more or 

 less suffused. 



The examples now before me from S. Vicente, which have 

 been regarded as the typical ones, are (on the average) smaller 

 and darker, and not quite so coarsely striated as those from S. 

 Antao. 



Helix serta. 



Helix serta, Alb., Mai. Bldtt. i. 215 (1854) 

 Dohrn, Mai. Bldtt. xvi. 7 (1869) 

 Morel., Journ. de Conch, xiii. 242 (1873) 

 Pfeij}., Mon. Eel. vii. 275 (1876) 



Habitat S. Nicolao ; a DD. Lowe et Dohrn inter Euphorbias 

 in monte Grordo lecta. An vere ab H. advena distincta ? 



Judging from the analogy of the H. erubescens in the Ma- 

 deiran archipelago, every island of which appears to harbour a 

 phasis more or less its own, I should be inclined to regard the 

 present shell as but an insular modification, peculiar to S. Ni- 

 colao, of the advena ; nevertheless if the latter in a more typical 

 state be really found in that island, as seems to be implied by 

 the remarks of Morelet, this supposition is perhaps scarcely 

 tenable, though I cannot but suspect that the particular form 

 to which he made allusion when he added ' cette variete [of the 

 //. advena'}, figuree dans la seconde edition de Chemnitz, parait 

 dominante a 1'ile San Nicolao ' may be the very Helix which we 

 are now considering, and which was described by Albers in the 



