268 TEST ACE A ATLANTIC A. 



sequans) albescens, sc. pallide albido-fulva aut flavo-cornea ; nec- 

 non sublongior, subgracilior, magis opaca, et plus minus erosa.] 

 S. (= A. Vulcani, Morel.) peristomatis margine dextro in 

 medio calloso, tuberculo plus minus distincte armato. 



Melampus sequalis, Lowe, Zool. Journ. v. 288. t. 13. f. 1-5 



(1835) 



Auricula sequalis, Id., Proc. Zool. Soc. Lond. 217 (1854) 

 Vulcani, Morel., Hist. Nat. des Acor. 207. t. 5. 



f. 8 (1860) 



Drouet, Faun. Acor. 167 (1861) 



Marinula sequalis, Paiva, Mon. Moll. Mad. 151 (1867) 

 Auricula Vulcani, Mouss., Faun. Mai. des Can. 135 



(1872) 

 sequalis, Watson, Journ. de Conch. 220 (1876) 



Habitat Maderse oras maritimas ; ad rupes sestu maris quo- 

 tidie submersas copiose adhserens. 



This is the universal Auricula on the tide-washed rocks 

 of Madeira ; and it is a species, evidently, of a considerable geo- 

 graphical range, occurring likewise at the Azores, Salvages, 

 and Canaries ; and it was found by Mr. Lowe not only at Mo- 

 gador, on the opposite coast of Morocco, but also at Lisbon. It 

 is extremely inconstant in colour, being sometimes of a rich 

 chestnut-brown, at others (indeed generally) of a paler or more 

 fulvescent hue, in which case it is on the average a trifle 

 larger, and sometimes (var. 7. albescens) of a dirty yellowish- 

 horn or whitish-yellow, under which last-mentioned aspect it 

 swarms at the Salvages (from whence I have just overhauled no 

 less than 1,580 examples, not one of which offers any appre- 

 ciable divergence as regards either colour or the relative deve- 

 lopment of the two ventral and one columellary plaits). These 

 somewhat albino individuals however from the Salvages are 

 usually a trifle narrower and more elongated in outline, and their 

 surface is not only less polished, but is also (as in the A. Pai- 

 vana) more or less eroded or (as it were) eaten-out into small 

 holes or cavities ; nevertheless since the form passes impercep- 

 tibly into the normal one, I cannot detect anything about them 

 to warrant a suspicion that they represent more than a slight 

 topographical variety of the ordinary Madeiran type. 



It is not only, however, in colour that the A. cequalis may 

 be said to be unstable ; for, however constant the two ventral 

 plaits may be, the outer lip of its aperture is liable to an 

 occasional thickening about the middle, a thickening which 

 is sometimes so strongly expressed as to shape out a conspicu- 

 ous tuberculiform callosity. Out of 1,584 specimens which I 

 have lately examined, only 36 have this tooth-like promi- 



