268 TEST ACE A ATLANTIC A. 



aequans) albescens^ sc. pallide albido-fulva aut flavo-cornea ; nec- 

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

 h. (= 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 eequalis, Id., Proc. Zool. Soc. Lond. 217 (1854) 

 „ Vulcani, Morel., Hist. Nat. des Agor. 207. t. 5. 



f. 8 (1860) 

 „ „ Drouet, Faun. Aqot. 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 adhaerens. 



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 IMorocco, but also at Lisbon. It 

 is extremely inconstant in colour, being sometimes of a rich 

 chestnut-browD, 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. eequalis 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- 



